Raheem Mostert has exited the 49ers' game against the Lions with a knee injury. San Francisco's starting running back was originally deemedquestionable to return after suffering the injury in the first quarter of the team's game against the Lions, but he was later Jarrett Stidham Jersey declared out.It's unclear on which play Mostert suffered the injury. He had two carries for 20 Dalton Keene...