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

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.

RB Jordan Mason, the NFL's leading rusher, suffered a sprained AC joint that is not considered serious during Thursday night's win at Seattle, but he will undergo further testing Friday.