Two recent Super Bowls are the ultimate example of how "next man up” can make or break an NFL football team. We saw many Chiefs offensive linemen go down last season. But Eric Fisher broke his Achilles in the AFC Championship Game. Andy Reid and his team couldn't save Patrick Mahomes who, in a disappointing loss to the Bucs, ran for his life most of the day. Although no team was able to handle as many injuries as the Chiefs' front line, it is clear that Andrew Wylie and Mike Remmers weren't the solution.You can see the opposite example if you go back a few decades. Near-MVP campaign of Carson Wentz carried the Eagles to the top in the NFC for most of 2017. However, Nick Foles took over when Wentz tore the ACL. Foles was terrible in his last two starts of regular season but he managed to throw for 972 yards and six touchdowns in three playoff games. The Eagles won a Super Bowl by having Wentz replaced.Every team is vulnerable in the salary-cap era. Let's take a look at the obvious vulnerabilities in the NFL and consider what organizations would do if their key player were to go.While a lot of these players are quarterbacks naturally, it is possible to lose a player at any position. As we saw with Chiefs last year, however, this can make or break your season. If a team has two or more starters, I will focus on the backup players. Unsurprisingly, however, I will start with a signal-caller.Next up: Logan Woodside and DeShone KizerLet's begin with the most obvious concern for any contending team. Tannehill's performance with the Titans is beyond any expectation since he arrived from Miami as a salary dump. Tannehill is both extremely efficient and easily accessible. Tannehill missed 21 games in Miami over his last three seasons due to knee and nerve problems, but he has not missed a single game since assuming the role of Tennessee's starter.Except for a moment when he fell while celebrating a touchdown, there hasn't been any need to give the Titans another quarterback. Tennessee could be in serious trouble if that happens. At best, its backups are questionable at the moment. Woodside was the 249th draft pick and had only three pass attempts in his career. Kizer, on the other hand, has a 58.9 passer rating over stints with both the Browns (and Packers)Last season, the Titans were able to get by without Woodside, and might be able again in 2021. However, losing Tannehill would make them a win-now team with one the worst quarterback situations in the league. Mike Vrabel's offense is run-heavy, so it might be possible to argue that they can get by with Woodside and Kizer if Derrick Henry is available. The Titans could be in similar bad shape if Henry is not there, considering that Henry's backfield includes Brian Hill, Darrynton Evans and Jeremy McNichols. Tennessee has a lot of top talent, but it will have to keep its stars healthy to live up the expectations.Next up: Cooper Rush and Ben DiNucci. Garrett GilbertThe 2020 Cowboys are a team with a high-profile roster that is prone to injuries. In training camp, Dallas lost Gerald McCoy, a free-agent signing. Then, the 2020 Cowboys saw their offensive line collapse, with star tackles Tyron Smith and La'el Collins playing just two games each, and Zack Martin missing eight. It was a grim picture that continued to worsen when Prescott, who had not missed a single professional start, sustained an ankle injury in Week 5. He would be out for the rest of the year.The Cowboys lack a proven quarterback after Dak Prescott. Photo by Tim Heitman/USA Today SportsAndy Dalton was appointed Prescott's replacement. He couldn't handle a patchwork team. Prescott and his linemen will be back in 2021. However, if Prescott is lost again, the Cowboys wouldn't have the ability to call upon someone as skilled as the Red Rifle. They have combined 80 pass attempts this season, which yielded a 52.5% completion rate and averaged 5.2 yards per try. Kellen Moore, the Cowboys' offensive coordinator, might have been better than Gilbert and DiNucci for spot starts last year. The Cowboys will not want to know if those backups have improved in 2021.Next up: Zech McPhearson and Michael JacquetCornerback is slightly different because a team may use two or three corners per snap. But let's keep in the NFC East to see a team who got what they wanted, and maybe regret it. The Eagles decided to trade for Slay, after years of focusing on depth rather than top-level talent and cutting corners. Slay was traded to the Eagles for the No. 1 corner, which fans had been waiting for. He signed a three year extension. Slay was inconsistent during his first season as an Eagles player, and the team lost around the talented corner.This team is dangerously thin at the corner, partly due to how much Slay is being paid. Avonte maddox, a hybrid defender, might be the first to start in the slot. However, the depth chart for cornerback around Slay's is among the lowest in the league. To compete for positions on the outside, the Eagles are seeking replacement-level corners and practice-squad players. Sometimes good corners come out of nowhere, but the Eagles don't want teams to count on finding a valuable player before the season begins.Jonathan Gannon, the new defensive coordinator, will need to be concerned about Slay's shutdown corner during his second campaign in Philly. These corners might not be able to hide if Slay isn’t on point or gets hurt. This is especially true in a division that has wideouts like Terry McLaurin, Kenny Golladay, and Amari Cooper.Next up: Barkevious mingo, Jacob Tuioti Mariner, Adetokunbo OgundejiFowler, like Slay, was a long-awaited player who failed to live up to his expectations in his new digs. Fowler, a former Jaguars and Rams pass rusher, managed just three sacks during a disappointing season in Atlanta. These three sacks tied for third place behind Deion Jones, star linebacker, and Grady Jarrett as the Falcons failed to field any player with even five sacks in 2020.ESPYS Pick'Em - Play for Free and Compete for $5,000Take Your PicksIn 2021, defensive coordinator Dean Pees must get more from his star edge rusher. Fowler was absent for two games last season. If he isn't available, Fowler would be unable to play on the edge. Jarrett is able to hold the middle, but the Falcons will be looking at midround picks outside for journeymen like Mingo and Jonathan Bullard. The Atlanta team is severely short on cap and desperately needs more edge support.Next up: Jalyn Jones, Patrick Jones, Janarius RobertsDid you see the 2020 Vikings season? Hunter was sidelined for the entire season because of a neck injury. The Vikings had Yannick Ngakoue as their starting quarterback, but the team decided to trade Hunter to the Ravens midseason. Minnesota had the fifth-worst adjusted rate of sacks in the league and was the third worst at avoiding pressure.Hunter is back and has signed a revised contract. Hunter will report to training camp in order to be available to play for the Vikings when the season begins. Although Hunter has been a tremendously productive player when he is available, the Vikings would not be able to play without their top pass-rusher. Minnesota added Sheldon Richardson in the summer but Holmes and Stephen Weatherly don't have enough pass-rushing talent. Although the Vikings took Robinson and Jones in the midround, they should not be expected to make significant contributions to their rookie campaigns.Next up: Deonte Harris and Marquez Callaway.Thomas did not miss 2020, but he suffered a high ankle injury in Week 1, which he never fully recovered from. After a six-game stint, Thomas returned to injured reserve. He was not a difference-maker in the postseason. Although the Saints were without Drew Brees and Emmanuel Sanders, the offense was fine. Jared Cook was also there.The Saints aren't as deep as Tre'Quan Smith and Michael Thomas. Rob Carr/Getty ImagesBrees Sanders, Cook, and Taysom Hill are gone. They have been replaced by Nick Vannett, Trevor Siemian and Kawaan Baker, seventh-round pick. Thomas will be the offensive's chain-mover in the air, regardless of whether it's Taysom Hill or Jameis Winston at quarterback. Tre'Quan Smith will be on the opposite side. However, if Thomas is unable to make it, Callaway & Co. would be available to fill in for Thomas.If they are able to find some cap space, it would not surprise them to pursue a veteran wideout at training camp.Next up: Geno Smith and Danny EtlingIt's likely that most Seahawks fans will be able to recall what it was like between Matt Hasselbeck's departure and Wilson arriving. This is why I think most fans weren’t happy to see Wilson leave the city this spring. Wilson rumors are over. Fortunately for Seattle fans, there have been few other quarterbacks with such a track record of being available. Wilson has not missed a single game in nine seasons due to injury. Peyton Manning is the only quarterback who has started every game for his team in his nine first seasons as a professional.Wilson has been through ankle injuries before. However, if anything more serious happened, the Seahawks will likely struggle to recover. Smith is their primary backup. Smith lacks Wilson's mobility, but has a career passer rating 72.9. Alex McGough and Etling have been able to bounce around the bottoms on pro rosters, but they never threw an NFL pass. If Wilson goes down, the Seahawks will need to retreat into a run heavy attack. This might be a good thing for Pete Carroll.Next up: Vinny curry, Kyle PhillipsLawson, the Jets' big-money free-agent defense addition this offseason is going to be the primary rusher for Robert Saleh. Although the Jets have Sheldon Rankins, who will play alongside Quinnen Williams, deep in the interior, Lawson is not expected to be injured or disappoint.Curry was an important Eagles player for stretches. However, he is a rotational edge at this stage of his career and does not have Lawson's athleticism. Saleh needs a "Leo"-lineman who is healthy. Consider that the 49ers dropped from second in adjusted Sack Rate with Nick Bosa in 2019, to 24th in 2018, after Bosa tore his ACL.Next up: Trace McSorley and Tyler HuntleyThe Ravens were able to see Jackson's life in his first two-plus seasons as a starter. Robert Griffin had to go into overtime against the Chiefs in Jackson's rookie season, and three backups threw passes for the Ravens last year.Griffin was Baltimore's primary bench player. However, if Jackson is lost, the Ravens would have to use McSorley to replace Jackson. Last season, the former Penn State player was 3-for-10. Marquise Brown was responsible for one of the passes, a touchdown of 70 yards to Brown.Next up: Cassius Marshall, Quincy RocheWatt is suddenly the top depth chart in Pittsburgh after the Steelers lost Bud Dupree in free agency to the Titans. As a 2020 third-rounder, Alex Highsmith impressed when he had to replace Dupree as a rookie. He is now a Defensive Players of the Year candidate. The starters are fine in an organization that is unrivaled when it comes to developing and drafting defensive players. What's the secret behind those two? But not so.The Steelers couldn't add much to the edge because of their cap problems. They used most draft picks to augment a flailing offense. Marsh was a three-year veteran of three teams last year and is currently on his eighth roster. Roche is a sixth-round rookie pick. While the Steelers have a lot of linebackers in their system, they usually only take those guys in the first few rounds. A Watt status change would put a win-now Pittsburgh team at risk. Highsmith is a promising player. But, would he be ready to be the greatest edge rusher in a Super Bowl contender's lineup?Next up: Roderick John, Charlie Heck, Geron ChristiansAlthough the Tunsil deal in 2019 may have sparked chaos in Houston, it is worth noting that Tunsil is still with the Texans as they rebuild their organization. The deal will be remembered as disastrous by the Texans. I don't know the quarterback, but Tunsil should do a great job protecting those snaps.David Culley, the new coach, could move Tytus Howard to his left side if Tunsil is injured. However, the Texans would be in one of the worst tackle situations within the league if they didn't have their costly addition.Next: Antwaun woods, Robert WindsorTo acquire Buckner, the Colts sent a 49ers first-round pick. The 7th overall pick fulfilled all expectations. Indy's first season, he racked up 9.5 tackles and 26 knockdowns, despite not playing a single game because he was on the COVID-19 roster. Buckner is the most expensive defensive player in the league. However, that's what teams want from their top interior pass rusher.DeForest Buckner was a great first season with the Colts but the Indy defense line is weak. MSA/Icon SportswireThe Colts are still questioning their edge with Justin Houston's departure in free agency. However, Buckner is crucial to the Colts being that force in 2021. Unsurprisingly, their sack rate as well as pressure rate were higher with Buckner on field. However, the passer rating they allowed rose to 107.2 with Buckner off the field. Grover Stewart, a fellow starter, isn't a pass rusher. The Colts also lost Denico Autry, an interior rusher, to the Titans in free agency.Next up: Foster Moreau and Derek CarrierWaller has been regarded as one of the best players in football and the Jon Gruden-era Raiders made the best move. The Vegas star has been Travis Kelce’s tight end for the past two seasons. They are ranked 1-2 in receiving yards and receptions, while No. 3 (George Kittle), is 64 receptions behind Waller and 654 yards ahead.Although Henry Ruggs is a top Raiders prospect, Waller could be a serious loss for them.Next up: Uchenna Fackrell, Kyler NwosuBosa was a difference-maker over his five first NFL seasons. Los Angeles' sack rate has been 6.3% with Bosa on field. It was 5.1% without Melvin Ingram, their first-round pick. The majority of this was due to Melvin Ingram being in the lineup. However, the 32-year old has since left the team and is still unsigned.Fackrell was the Chargers' only replacement for him. Despite a disappointing 10.5-sack season in 2018, Fackrell has 10 sacks in his four previous seasons.Next: Chad HenneIt is obvious that any team will lose their most talented quarterback. It might be interesting to discuss whether other Chiefs have faced a similar situation. Travis Kelce recently finished what is arguably the greatest season in league history for a close end, with Nick Keizer and Noah Gray as his backups.Similarly, if Tyreek Hills pulled a hamstring the Chiefs might suddenly be looking at a receiver depth chart that included Mecole Hardman and Demarcus Robinson as well as Cornell Powell, Byron Pringle, and Cornell Powell. Mahomes cannot be kept off this list. I try to limit it to one player per team. However, the Chiefs may have three of most important players in the league on the one side.Next up: Blaine Gabbert and Kyle Trask. Ryan GriffinIt makes perfect sense to end up with the best ever, doesn't it? Brady was able to immediately transform the Bucs' offense in 2020. The legendary quarterback became more comfortable with each year, and he won his seventh Super Bowl. Although the Bucs have a lot of talent, many of those same players were also on teams with Jameis Winston at quarterback and Ryan Fitzpatrick at receiver, and these offenses were much better in fantasy football than real life.play 1:03. What is Brady's motivation for his 22nd NFL season. Bart Scott believes that Tom Brady wants to be remembered as an outstanding athlete, like Wayne Gretzky or Muhammad Ali.Brady was remarkably healthy throughout his career, with two exceptions related to his knee. Brady, the future Hall of Famer, was injured in his knee in 2001 and missed the AFC Championship Game. He then missed the last 15 games of 2008 after tearing the ACL in the opener. Although I don't see any signs that he is in decline, we don't know when. Remember that Brett Favre, then 40, was a Pro Bowler in 2009. He brought the Vikings within one touchdown of the Super Bowl. His streak of consecutive games ended due to a shoulder injury. He threw more interceptions and touchdowns, and he retired at the conclusion of the campaign.The Bucs would be in a bad place if Brady was to fall off the proverbial edge. Gabbert is a Bruce Arians favourite, but the former Jags first round pick has a 72.3 career passer rate. Tampa selected Trask in Round 2 to replace Brady. However, it would be a big ask for Trask to take over as rookie and become the most successful player in league history. The good news is that the Bucs won't have to discover what's behind these other doors.