Manager Alex Cora said after Wednesday's game versus Tampa Bay that Jansen is dealing with a shoulder injury, Pete Abraham of The Boston Globe reports.
Jansen struggled with command issues and decreased velocity during his outing Wednesday, which prompted a visit from Boston's training staff with two outs in the ninth inning. He was able to remain in the game and secure his 27th save of the season, but it's possible the Sox make the 36-year-old unavailable out of the bullpen over the next few days due to his shoulder.