The team said Tuesday that Janssen had the procedure Friday in Los Angeles to repair lingering joint soreness. The 31-year-old had the small portion of the end of his clavicle shaved down to relieve the discomfort.
Janssen was thrust into the closer role last season after an injury to Sergio Santos, and he thrived in the position.
Janssen converted 22 of 25 save opportunities while posting a 2.54 ERA. He had 67 strikeouts and just 11 walks over 63 2/3 innings.