49ers' Mason day-to-day with sprained AC joint

San Francisco 49ers running back Jordan Mason suffered a sprained AC joint in the team's 36-24 win over the Seattle Seahawks on Thursday, head coach Kyle Shanahan announced Friday.

Mason is considered day-to-day, Shanahan added.

Mason has been a key contributor to the 49ers' offense with reigning Offensive Player of the Year Christian McCaffrey sidelined to begin the campaign. The Georgia Tech product leads the league in both rushing yards (609) and carries (114) and also has three rushing touchdowns.

Rookie Isaac Guerendo and Patrick Taylor are next in line for running back snaps if Mason is forced to miss time and McCaffrey remains sidelined. The 49ers also have veteran Ke'Shawn Vaughn on their practice squad.