Mason (undisclosed) won't play in Sunday's preseason game against the Saints, Eric Branch of the San Francisco Chronicle reports.
Mason is dealing with what is being described as a minor injury. The 49ers are thin at running back with Christian McCaffrey (calf), Elijah Mitchell (hamstring) and Isaac Guerendo (hamstring) all banged up as well, leaving more opportunities for Patrick Taylor, Matt Breida, Cody Schrader and Ke'Shawn Vaughn.