12:00 PM PT -- 9/14 -- Mostert now says he'll miss the rest of the season due to his knee injury.
"After consulting with multiple doctors and weighing my options, I will be having season-ending surgery to repair my knee."
Mostert added he's hopeful the procedure will allow him to come back at "110%" next season.
"Thank you for your support in our decision," the running back said. "I'M FAR FROM DONE!"
12:54 PM PT -- The news is in ... Mostert will likely miss at least 8 weeks with torn knee cartilage. Huge bummer, but get back soon, Raheem!!
Raheem Mostert was engulfed by hate messages from fans after the NFL star suffered an injury Sunday ... with the RB's wife saying people said the Niners player "should kill himself."
Devon Mostert spelled it all out in an emotional social media post hours after the 49ers beat the Detroit Lions ... saying she and her hubby received "THOUSANDS" of terrible comments following the game.
In her post, Devon said some of the messages suggested Mostert be cut from the team ... while others made fun of his injury history.
"I know I shouldn't care, but wow. Wow wow wow," Devon said. "The nasty things some of you just carelessly say is gut wrenching. I don't think ya'll get it. Football is my husband's job. It's how my family EATS. To read such HEARTLESS and degrading comments about the person I LOVE hurts."
Devon continued, "And I try so hard to shake them off... I do. But when there's HUNDREDS, THOUSANDS. It's a lot."
Mostert played just a handful of snaps against the Lions, recording two carries for 20 yards before hurting his knee.