Mitchell entered the concussion protocol Monday, Nick Wagoner of ESPN.com reports.
Mitchell was checked for a concussion in the fourth quarter of this past Sunday's loss at Seattle but was cleared to return. He eventually finished with 22 carries for 66 yards and one touchdown and added three catches (on three targets) for 18 yards. Having said that, coach Kyle Shanahan relayed that Mitchell reported concussion symptoms Monday morning and now will be subject to the five phases of the protocol for head injuries to receive clearance for game action. Mitchell's activity level thus will be of keen interest once the 49ers resume practicing midweek. If he's able to log a limited session Wednesday and/or Thursday, he'd be trending in a positive direction ahead of Sunday's game at Cincinnati.