Coleman was splitting carries with Mostert throughout the first half and left with 21 yards on six carries.
The fifth-year running back fell awkwardly on his right arm at the tail end of a 4-yard run in the red zone with 9:44 left to go in the first half. San Francisco scored on the very next play to go up 17-0. The 49ers ended up winning, 37-20.
Coleman led San Francisco on the ground in last week's win over the Minnesota Vikings, gaining 105 yards and two TDs on 22 attempts. Without Coleman, San Francisco relied heavily on Mostert, who set multiple records in rushing for 220 yards and four rushing touchdowns; Matt Breida added one carry for two yards.