49ers running back Eli Mitchell officially placed on IR with knee injury

September 13 update: The 49ers have officially placed Mitchell, who is expected to miss two months with the knee injury he suffered in Week 1, on injured reserve. That’s going to rule him out for eight games, which is the timeline of his recovery.

Update: Mitchell was seen leaving the locker room with a substantial brace on his right leg, per Jennifer Lee Chan.

San Francisco 49ers running back Elijah Mitchell is out for the rest of the game against the Chicago Bears with a knee injury, per the team’s official Twitter account.

Mitchell had been banged up in the preseason but was declared active for this game. He finished with six carries for 41 yards and wasn’t targeted in the passing game. The field at Soldier Field in Chicago was underwater pregame from the rain they had. It is unclear when Mitchell sustained the injury. He likely tweaked it during the game, and the 49ers felt no pressure to force him back in to aggravate it further.

The 49ers once had a deep running back room but through roster decisions, trimmed the position down. The main backup is Jeff Wilson Jr. The third-down running back is Jordan Mason, and the rookie Tyrion Davis-Price would’ve been behind them but was inactive for the game. It will be up to Wilson Jr. and Mason to take the 49ers the rest of the way against Chicago.