The 49ers' Week 1 win over the Detroit Lions came at a tremendous cost.
First, the 49ers learned they lost starting cornerback Jason Verrett for the season with a torn ACL. Now, the 49ers have learned they'll be without starting running back Raheem Mostert for at least the next eight weeks with a cartilage injury in his knee that will require surgery. The 49ers will place Mostert on the Injured Reserve List this week.
Mostert carried the ball only twice Sunday against the Lions, and looked terrific on both carries. It's unclear when exactly he suffered the injury, although it's possible his knee was compromised during the offseason. For what it's worth, Mostert wore a big, bulky knee brace every day in camp. He insisted at the time that he wasn't injured, but now you can't help but wonder.
Losing Mostert is a tremendous blow to the 49ers offense, because he's their most explosive player. He's the second fastest offensive player in the NFL after Tyreek Hill, and the biggest threat the 49ers have to score a 90-yard touchdown. Mostert makes everything so easy for them.
But the 49ers still have good running backs. They have rookie sixth-round pick Elijah Mitchell, who rushed for more than 100 yards Sunday in his NFL debut and looked like a mini version of Mostert. The 49ers also have second year undrafted free agent JaMycal Hasty, who's promising, as well as rookie third-round pick Trey Sermon, who was a healthy scratch against the Lions but will have to play some of the time the next eight weeks.
Halfway through the season, Mostert should return, as well as Jeff Wilson Jr., who's out with a torn meniscus.