Mason injured his shoulder in the second quarter of the 49ers’ Week 6 win over the Seattle Seahawks. He returned for the second half, but exited after aggravating the shoulder on the first play of the third quarter. He spent the remainder of the game on the sideline and head coach Kyle Shanahan didn’t have much information after the game.

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

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.