Mitchell is under evaluation for a head injury during Sunday's game in Seattle, Matt Maiocco of NBC Sports Bay Area reports.
Mitchell took an elbow to his helmet on a carry late in the third quarter on which he lost the ball. Ultimately, a fumble was overturned as his knee was down before the ball came loose, but the running back required immediate medical attention and went to the blue sideline tent to be examined. If he's unable to return, Mitchell will end Week 13 with 18 carries for 54 yards and one touchdown and two catches (on two targets) for seven yards. Jeff Wilson and JaMycal Hasty are the other healthy RBs on the 49ers' active roster.