Coach Kyle Shanahan said Mostert (knee) will be held out of practice Tuesday, Matt Barrows of The Athletic reports.
Both Mostert and Matt Breida (ankle) will be non-participants, leaving Tevin Coleman and Jeff Wilson as the 49ers' only healthy running backs. There seems to be a chance that Breida won't play Thursday, so if Mostert gets the all-clear to suit up Thursday, he could be the No. 2 or No. 3 RB in what has been an explosive ground attack this season.