Janssen signed a minor league contract with the Red Sox on Wednesday, Pete Abraham of the Boston Globe reports.
Janssen will first report to Short-Season Lowell before joining the team's Triple-A Pawtucket affiliate. A former closer, Janssen last pitched in the majors in 2015 with the Nationals and was granted his release from the Padres after spring training this season. If all goes well in his minor league appearances, the veteran reliever could join the Red Sox's bullpen down the road.