Raheem Mostert Injury: Fantasy Impact for Elijah Mitchell, Trey Sermon & JaMycal Hasty

49ers running back Raheem Mostert is headed to IR and will be out eight weeks with a knee injury

Fantasy managers with stock in 49ers running back Raheem Mostert are all too familiar with his spotty injury history. The latest addition to that is chipped cartilage in his knee. Coach Kyle Shanahan said the expectation is for Mostert, now placed on injured reserve, to miss eight weeks.

#49ers RB Raheem Mostert has chipped cartilage in his knee. He will go on IR. Kyle Shanahan said expectation is about eight weeks for Mostert to return.

— Nick Wagoner (@nwagoner) September 13, 2021

Mostert left San Francisco’s win over the Lions on Sunday after taking two carries for 20 yards. He did not return. What preceded that injury and followed it make the running back situation for the 49ers — stop me if you’ve heard this before — complicated. Prior to the game, rookie Trey Sermon was announced a surprise inactive.

And then there’s what happened after the injury: Mitchell ran for 104 yards on 19 carries and a score. Meanwhile, JaMycal Hasty took his lone carry of the day for a three-yard touchdown and added a 15-yard catch.

Figuring out which running back will be “the guy” — or if there will even be a guy or a dreaded committee — can be guesswork considering Shanahan’s track record with running backs. 

So let’s try to make sense of the situation in San Francisco:

Raj Mehta/USA TODAY Sports

Elijah Mitchell

Mitchell is the top target in this backfield until proven otherwise. All we have to go off is one game, but he handled 19 of the team's 28 carries in his debut and showed some explosiveness with a 38-yard run. The rookie rusher is a sixth-rounder out of Louisiana, where he ran for 3,267 yards across four years.

The 2020 Sun Belt first-teamer clearly made a case for himself on Sunday and earned Shanahan's trust when given the opportunity. Mitchell ended up playing 64% of offensive snaps and graded out well among all running backs Sunday. According to PFF, he forced six missed tackles (second-most), had three rushing of 10 or more yards (tied for second) and had 73 yards after contact (third). Ahead of Monday night football, Mitchell is the RB13 for Week 1. He is a priority add despite possible competition.

Trey Sermon

The decision by Shanahan for Sermon not to play Sunday is a huge indictment of the third-round rookie's performance to date. With Mostert sidelined, we should at least see Sermon play in the weeks to come, but it's unclear how much of Shanahan's trust in him is as low as it seems. Mitchell commanded the lion's share of the 49ers' carries, with quarterbacks Jimmy Garoppolo and Trey Lance tying for second on the team with three apiece. Sermon ran for 2,946 yards across four years at Oklahoma and Ohio State and famously shredded Northwestern for 331 yards rushing in the Big 10 Championship Game.

Sermon became something of a fantasy darling in the offseason with the expectation he would eventually surpass Mostert as the starter in one of the best rushing offenses in the league, not unlike the situation in Denver with Javonte Williams and Melvin Gordon. Shanahan said after the game that Mitchell and Hasty beat out Sermon in training camp and preseason. It appears Sermon has a lot of work to do to carve out a meaningful role in the 49ers' offense to ascend to fantasy relevance. Hold tight, owners of Sermon stock.

JaMycal Hasty

Hasty was fourth on the team in total yards a season ago as a rookie. However, the three players who finished above him are either injured (Mostert and Jeff Wilson Jr.) or no longer with the team (Jerick McKinnon). Hasty played 29% of the team's snaps and finished with just two touches. Unless the injury bug strikes this backfield again, Hasty is best left on waivers.

Jeff Wilson Jr.

Things are going to get interesting in six to eight weeks when Wilson and Mostert could return. Wilson led the team in rushing yards, carries and touchdowns despite only playing 12 games last season. He underwent offseason surgery to repair a torn meniscus and will miss at least the first six games of the season.

Wilson’s status five weeks (or more) from now, which feels like years in fantasy time, should not affect how much you spend to add Mitchell. But it is a situation worth monitoring, especially since his return would line up with Mostert’s.