Coach Kyle Shanahan relayed Tuesday that Mitchell is dealing with a strained hamstring, Lindsey Pallares of the 49ers' official site reports.
Meanwhile, Christian McCaffrey has a calf strain that figures to sideline him a couple of weeks and Isaac Guerendo has also been slowed by a hamstring issue. To bolster their backfield depth, the 49ers have added Matt Breida to the mix. Once Mitchell returns to the field, he'll look to cement his standing as McCaffrey 's top backup.