There was an injury that caused the absence of the man who missed Saturday's draw at Villa.
The interim boss of Manchester United says he makes decisions in the best interest of the team.
The Portuguese forward was brought off with 20 minutes to go as United was 2-0 up.
As he came off,Ronaldo threw his coat to the ground and sat on a step in the dugout.
The reaction to being taken off was normal.
He came back from an injury and was not happy. I was happy to have him with me for the game after Edinson Cavani couldn't train.
The Portugal captain missed the match at Villa due to an injury, and the experience of losing a two-goal lead late in the game drove the decision to substitute him.
After being 2-0 up with 13 minutes to go, United drew 2-2 at Villa Park, and Rangnick wanted to avoid a similar collapse in west London.
"Ronaldo was told that we had to learn from Villa Park," said Rangnick. I was angry with myself for not changing to a back five.
I did not want to make the same mistake again. I said that when you are a head coach, you will see it through the glasses.
My job is to make the best decisions for the team and the club and I hope he sees that.
'Ronaldo provided unnecessary sideshow'
The chief football writer is Phil McNulty.
When Rangnick decided to removeRonaldo with 20 minutes left, Manchester United were well in control.
It was perfectly logical in the circumstances, but we were treated to a full range of amateur dramatics as he walked off at a snail's pace, shaking his head and having a rather comical struggle with his coat.
This was not a happy person. His ego provided a completely unnecessary sideshow to United's win, which was pretty much sealed by the time he was taken off.
As he was unmoved by the anger of the man, he was completely justified in his decision.
The interim manager leaned over to give the Portuguese an explanation for his decision. Not that he needed to. The explanation was enough for Rashford's goal.
It was a pointless exhibition by a player who, for all his brilliance, still gives off the air of a player and personality who almost thinks he is bigger than Manchester United.
When the manager's change worked so well, it's no good for him to do such antics.
It's not the first time this season that the ego of the player has trumped team considerations. The explanation that he was preserving the 36-year-old for the games ahead was more acceptable than his superstar's behavior.
Even though he may still be able to produce those flashes of genius, as he did in the build-up to United's second goal, he is not the athlete he was and sometimes needs protecting from his desire to play every minute of every game.
It is a poor look when he shows disrespect for a manager's decision, so it never does any harm to remind him that Manchester United are not run for his benefit. The dog does not wag its tail.
The person got it right. The person got it wrong.
The boss was impressed by Elanga and De Gea.
Anthony Elanga scored his first goal of the season.
Three of Manchester United's four goals at Brentford were scored through the club's academy.
The manager revealed that he refused to send the teenager out on loan in the January transfer window.
"From the very first day of training, he showed up, and I thought he was really good," said Rangnick.
He was on his way out. I told him that he would stay here. He's developed in training.
At the half-time break, United were fortunate to go in goalless as they missed many chances and saw three saved by David de Gea.
The Spanish goalkeeper was angry when he failed to keep a clean sheet as Ivan Toney scored a late goal for the home side.
He has been making great saves in the first half over the last couple of weeks. I think he is one of the best keepers in the world.