SANTA CLARA — Raheem Mostert fractured his right forearm during the 49ers' 34-3 win over the Oakland Raiders, and coach Kyle Shanahan said he assumes the running back will miss the remainder of the season.
Mostert left the field with his right arm in an air cast in the middle of the third quarter.
At the time of his injury, Mostert was the game's leading rusher with seven carries for 86 yards. His 52-yard touchdown run was the longest of the day as well.
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Mostert has shared the load with Matt Breida, who has been dealing with an ankle injury for several weeks. Both running backs were thrust into action after Jerick McKinnon suffered a season-ending ankle injury in the last week of the preseason.
This season, Mostert has carried the ball 34 times for 261 yards, good for an average of 7.68 yards per carry.
If Mostert indeed can't return, the 49ers also will miss him on special teams, where he is one of the top contributors in the NFL.