Niners running back Raheem Mostert will be placed on the injured reserve and is set to miss approximately eight weeks with chipped knee cartilage, coach Kyle Shanahan announced.
Mostert completed only four snaps and recorded 20 yards on two carries, before leaving in the first quarter of the team's 41-33 win over the Lions on Sunday. He was originally listed as questionable but the Purdue alum was later ruled out by halftime. After the game, Shanahan confirmed that it wasn't an ACL injury.
In his stead, rookie running back Elijah Mitchell, a sixth-round pick out of Louisiana, put together an impressive NFL debut with 104 yards and a touchdown on 19 carries.