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.

Mason has 10 days to prepare for the 49ers' Week 7 matchup against the undefeated Kansas City Chiefs. If Mason isn't able to suit up, the 49ers will rely on rookie running back Isaac Guerendo and fourth-year running back Patrick Taylor Jr.

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