According to league sources, the San Francisco 49ers running back is going to be out about two months with a knee injury.
The Niners lost to the Bears 19-10) at Soldier Field.
It wasn't immediately clear how Mitchell got hurt, though his last snap before the injury was a touchdown by Samuel. A Bears defender rolled into the back of his legs as Mitchell was blocking for Samuel.
Mitchell carried the ball for 41 yards before leaving. Mitchell didn't play in the preseason because of a hamstring issue, but he has dealt with a lot of injuries in his two years in the league.
Jeff Wilson Jr. took Mitchell's place as the primary running back. Wilson and Samuel carried the load for the Niners, with Wilson and Samuel carrying the load for 22 and 52 yards, respectively.
The third-round draft pick out of LSU is on the 53-man roster.
This report was based on information from Nick Wagoner.