Mostert (knee) was limited in practice Wednesday, Nick Wagoner of ESPN.com reports.
Mostert got back on the field for the first time since spraining his MCL in Week 2, but he may have to bump up to full participation by week's end to gain clearance to play from the 49ers' medical staff. If he misses a third consecutive contest Sunday against the Dolphins, the 49ers backfield will be manned by Jerick McKinnon, Jeff Wilson and JaMycal Hasty.