Mostert (ankle) was listed as a non-participant on the 49ers' estimated injury report Monday, Matt Maiocco of NBC Sports Bay Area reports.
Prior to Sunday's 12-snap showing in Arizona, Mostert racked up 29 touches for 174 yards from scrimmage in the previous three games. Perhaps the ankle injury was to blame, but he worked with Alfred Morris (11 offensive snaps) behind starter Matt Breida (31) in Week 8. With a short week to prepare for a Thursday night Bay Area battle versus the Raiders, Mostert could be relegated to a fringe role yet again if the issue is serious.