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Raheem Mostert announces he’s having season-ending surgery to repair his knee

Kyle Shanahan initially announced Mostert would return in eight weeks on Monday. To replace him, the 49ers are signing RB Kerryon Johnson to the practice squad.

Las Vegas Raiders v San Francisco 49ers Photo by Ezra Shaw/Getty Images

The San Francisco 49ers knew they’d be without starting running back Raheem Mostert for at least eight weeks after they found out Mostert had “chipped knee cartilage.”

Kyle Shanahan said that he anticipated Mostert would return to the team in eight weeks. However, after consulting with multiple doctors and weighing his options, Mostert announced on Twitter Monday that he’s having season-ending surgery to repair his knee:

After one game, the 49ers have lost two critical starters in Mostert and Jason Verrett.

Elijah Mitchell impressed, but Mostert has proven to be the fastest player in the NFL with the ball in his hands and has been dominant when he’s on the field.

How will the 49ers backfield look moving forward? It’s tough to say. They’ll rely on two rookies until Jeff Wilson returns.

Based on Sunday’s game, they’ll need to find a third-down back. JaMycal Hasty allowed a couple of pressures blocking. Thankfully, Jimmy Garoppolo made the most out of each play, but that’s not something you want to rely on.

Per Aaron Wilson, formerly of the Houston Chronicle, the 49ers are working out running back Artavis Pierce.

Pierce, 5’11, 208 pounds, was an undrafted free agent out of Oregon State in 2020. He played for the Chicago Bears, practice squad through last week before being waived. Pierce appeared in three games with the Bears last season. He had six carries for 34 yards. One of those went for 23 yards and a touchdown.

Here’s Pierce’s scouting report from The Ringer’s Benjamin Solak:

PROS: Long-strider who has great long speed to rip through the first level. Size is enough that he can lower a shoulder and deliver blows/break tackles in the second level with linebackers. Returner background illustrates a great space player who has a knack for space and good wiggle. Agility doesn’t overwhelm, but it’s solid. Shows a good ability to stay patient behind his blockers on power concepts and isn’t always suckered in by immediate space. Has hands to take on more receiving reps.

CONS: Does not yet have good vision and is very limited in terms of what concepts he can run. Bangs his head into a wall on zone flow despite nice profile for successful zone running—anticipation a question mark here. Limited exposure as a pass-catcher or pass blockers—will be seeing first year of significant starts.

At his Pro Day, Pierce ran a 4.47 40-yard dash, but each of his other times was below average.

We all wish Mostert a speedy recovery. But, since he’s in the final year of his contract, will the 49ers re-sign Mostert?

Per Adam Schefter, the 49ers are signing former Lions running back Kerryon Johnson to the practice squad. Johnson had 52 carries for the Lions in 2020 for 181 yards, which is good for 3.5 yards per carry. He was much better through the air. At 24, Johnson could help the 49ers now and in the future.

A knee sprain (2018) and a Meniscus tear (2019) stalled the projection of his career. He’s not the same player and has a pretty length injury history, including shoulder injury dating back to college.