49ers' Jordan Mason: Aggravates shoulder injury

Head coach Kyle Shanahan said Monday that Mason aggravated his existing left shoulder sprain in Sunday's 30-24 win over the Cowboys and is viewed as day-to-day, Nick Wagoner of ESPN.com reports.

Shanahan said Mason could have returned to the game after he went to the locker room just before halftime. Mason, however, never played another snap, as Isaac Guerendo handled backfield duties the rest of the way. With Christian McCaffrey (Achilles) trending toward a return from injured reserve after the 49ers' Week 9 bye, Mason's days as San Francisco's lead back appear to be either numbered or over.