49ers running back Jordan Mason got off to a strong start Thursday night, but he wasn’t there 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.

ESPN’s Adam Schefter reports that Mason has been diagnosed with a sprained AC joint. The injury is not considered serious but Mason is undergoing further tests.

The initial diagnosis is good news for the 49ers, and rookie Isaac Guerendo’s performance likely makes them feel better, too. Guerendo had 10 carries for 99 yards, including a 76-yard run that set up the game’s final touchdown.