The 49ers wouldn't have beaten the Seahawks this past Thursday night without rookie running back Isaac Guerendo. The 49ers had a 20-point lead, but starting running back Jordan Mason left the game with a sprained AC joint in his shoulder.

Following a 14-yard run, Mason appeared to be in pain on the field in Seattle. After being looked at on the field, Mason exited the game and went back to the locker room with the 49ers training staff in Seattle.

Additionally, 49ers backup running back Elijah Mitchell is out for the year due to a hamstring injury. That has paved the way for Mason to take the reins of the backfield — and