Raheem Mostert has exited the 49ers' game against the Lions with a knee injury. San Francisco's starting running back was originally deemed questionable to return after suffering the injury in the first quarter of the team's game against the Lions, but he was later declared out.
It's unclear on which play Mostert suffered the injury. He had two carries for 20 yards before he left the field.
The 49ers are suddenly very thin at the running back position in wake of Mostert's injury. The team dressed just three running backs on Sunday, including Mostert. With Mostert out of action, the 49ers have only JaMycal Hasty and rookie Elijah Mitchell active. The team's third-round rookie, Trey Sermon, is inactive for the game.
Hasty, 25, is a second-year back who played eight games for the 49ers in 2020. He totaled 148 rushing yards and a touchdown on 39 carries and also played 62 special teams snaps.
Mitchell, 23, is a sixth-round 2021 draft pick who played collegiately at Louisiana. He had 46 touchdowns during his college career and ran for a 38-yard touchdown after Mostert exited the game.
It will be interesting to see if Mitchell continues to get carries with Mostert sidelined and Sermon inactive. If so, he may make a case to be the team's backfield leader, depending on how long Mostert will be out.
UPDATE: NFL Network's Ian Rapoport reports that Mostert will be out for at least eight weeks after chipping cartilage in his knee. He will be placed on IR as a result of the injury.