49ers' Raheem Mostert to Undergo Surgery for Broken Arm Injury | News, Scores, Highlights, Stats, and Rumors

Shanahan later announced Mostert would undergo surgery Friday and be placed on injured reserve.

Mostert, 26, went down on a gruesome third-quarter play that saw his arm bend in the wrong direction. Multiple players took a knee while trainers tended to him, putting Mostert's arm in a brace before he was taken off the field.

Mostert rushed for 86 yards and a touchdown on seven carries before he exited. He had carved a solid role in recent weeks as a change-of-pace back, rushing for 50-plus yards in three of the last four games.

Injuries have overwhelmed the 49ers. Their original starter at running back, Jerick McKinnon, suffered a torn ACL in the preseason. Fill-in starter Matt Breida has dealt with an ankle injury, and the team lost quarterback Jimmy Garoppolo for the season to a torn ACL in Week 3.

Every time something positive happens for this team, another injury cancels it out. Mostert is just the latest example.