RB Jordan Mason filled in admirably to start the year, but he was hit with a shoulder injury in Week 6 that he battled until McCaffrey’s return in Week 10. McCaffrey and Mason were both hurt in a Week 13 loss to the Buffalo Bills, which pushed rookie fourth-round pick RB Isaac Guerendo into the starting role.

The 49ers will have to start their fourth different running back this Sunday against the Miami Dolphins. That's because rookie running back Isaac Guerendo is likely to miss Sunday's game with a hamstring injury he suffered this past Thursday night.

San Francisco 49ers running back Isaac Guerendo appeared on Wednesday's injury report due to a hamstring issue sustained during last week's game against