Mostert is likely out for the season after fracturing his right forearm in Thursday's win over the Raiders, Matt Maiocco of NBC Sports reports.
While he is not officially out for the season, head coach Kyle Shanahan assumes it is the case for Mostert given the gruesome nature of the injury. If he does land on injured reserve, he will be joining fellow running back Jerick McKinnon (knee), leaving the 49ers with Alfred Morris and Matt Breida as the only healthy options currently on the roster. Expect the team to bring in a free agent back or promote one from the practice squad before next Monday's matchup with the Giants. Mostert had his best performance of the season before exiting the contest, recording 86 yards and a touchdown on seven carries.