San Francisco 49ers running back Raheem Mostert announced on Twitter that he will miss the rest of the 2021 season after electing to undergo knee surgery. He shared an emotional message to address just how disappointed his is to miss the year.

Coach Kyle Shanahan told reporters Mostert had chipped cartilage in his knee during a recent press conference, but thought the running back could be back this season. Apparently, that won’t be happening, with Mostert revealing he cannot return this year.

“This (surgery) gives me, without a doubt in my mind, the best possibility at coming back 110%,” he wrote Tuesday. “I’m gutted. … This is obviously not what I worked so hard for. I wish more than anything I could be out there on the field.”

💔 pic.twitter.com/Udsl4aTuAq

— Raheem Mostert (@RMos_8Ball) September 14, 2021

Not long after Mostert’s announcement, the 49ers added running back Kerryon Johnson to their backfield. He will join Elijah Mitchell, JaMycal Hasty, Trey Sermon and Jeff Wilson Jr. (PUP list) in San Francisco’s backfield.

And with RB Raheem Mostert announcing today that he is out for the season with a knee injury he sustained vs. Detroit, the 49ers now are signing former Lions’ RB Kerryon Johnson to their practice squad, per his agent @DrewJRosenhaus.

— Adam Schefter (@AdamSchefter) September 14, 2021

Here’s hoping Mostert returns at full strength. His breakout story is one of the NFL’s best.