Report: Jordan Mason believed to have sprained AC joint in shoulder

49ers running back Jordan Mason was off to a strong start on Thursday night, but he wasn't around for the end of the team's win. Mason injured his shoulder in the first half and was forced out of the game after one carry early in the third quarter. Mason had 73 yards on eight carries before leaving the game.Adam Schefter of ESPN reports that Mason has been diagnosed with a sprained AC joint. The injury is not considered to be a serious one, but Mason is still undergoing further tests. The initial diagnosis is good news for the 49ers and the performance of rookie Isaac Guerendo likely makes them feel better as well. Guerendo had 10 carries for 99 yards, including a 76 yard run that set up the final touchdown of the game.