Mattingly wouldn't say if surgery was an option, only that "everybody is comfortable that we've decided the best way to go." League was examined by team doctor Neal ElAttrache and one other doctor in Las Vegas, site of a national orthopedic surgeons convention.
League hasn't pitched since March 9. Two days later he had an extended bullpen session, after which he felt the discomfort. He had a cortisone injection and tried two bullpen sessions, but more discomfort led to a contrast MRI on Wednesday.
League's absence can be mitigated by the glut of relievers pitching well in camp after management spent the winter stockpiling them.
League hasn't had a disabling shoulder injury since 2007. The ground-ball specialist turned in an off-the-radar solid season in 2014, with a 2.57 ERA in 63 appearances.
Mattingly said Chad Gaudin, who had an MRI on Thursday for continued nerve issues in his right arm, would be shut down as doctors evaluate results. He expected more information by Monday.
The suspicion is that Gaudin's injury is related to a condition that led him to undergo a foraminotomy procedure by back specialist Robert Watkins last year to relieve pressure on a nerve in his neck that caused a loss of feeling and dexterity in his hand and forearm. He missed the entire season.
Gaudin, a late signing to a Minor League contract, was viewed as a potential swingman, but now is out of the competition to make the club out of Spring Training.
With League and Gaudin sidelined, the Dodgers have 12 pitchers vying for seven or eight spots. Relievers still in camp are Chris Hatcher, J.P. Howell, Joel Peralta, Juan Nicasio, Pedro Baez, Yimi Garcia, Adam Liberatore, Paco Rodriguez, David Aardsma, Mike Adams, David Huff and Sergio Santos. Huff has a decent chance to make the club as a swingman who can start in place of the injured Hyun-Jin Ryu.
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.