Mostert was diagnosed with another high-ankle sprain during the team’s Week 15 loss to the Cowboys.
He finishes his season with 521 rushing yards and three total touchdowns in eight games, having missed one game early in the season with a knee injury before the first high-ankle sprain sidelined him.
The 49ers have Jeff Wilson Jr., Tevin Coleman and Jerick McKinnon remaining at the position. With Austin Walter on the COVID-19 reserve list, the 49ers signed running back Tyler Gaffney to the practice squad.
“The plan with the running backs is, whoever’s healthy is going to be up,” Shanahan said, via Josh Schrock of NBCSportsBayArea.com. “Raheem’s down. I think Jeff [Wilson Jr.] got out of the game healthy enough. Tevin’s getting better each week. Jet’s been there for us every game, and Walter is on COVID. I think he gets cleared that day. The odds of us playing him that day probably aren’t too high, but we’ll see. Hopefully, we don’t lose anyone else during the week.”
Samuel’s hamstring injury ends his season. He played seven games, gaining 417 yards and scoring one touchdown on 41 touches.
The 49ers listed several players out of practice on their estimated injury report, including defensive tackle Javon Kinlaw (knee), cornerback Richard Sherman (calf), defensive end Dion Jordan (knee), safety Tarvarius Moore (knee) and safety Jimmie Ward (concussion).