Angels pitcher Garrett Richards had a stem-cell injection in his right elbow on Monday.
Manager Mike Scioscia says there's no timetable for his return. The right-hander went on the 15-day DL on May 6, leaving the injury-riddled team without their best starting pitcher.
Richards decided on the injection as a way to avoid surgery for the torn ligament in his arm, although it will be weeks before he knows whether it worked.
''Hopefully it's going to be the course of action he needs to heal and get back to action,'' Scioscia said. ''Really he doesn't have many symptoms at all so I know that he's confident that he'll heal with this course of action.''
Scioscia said if Richards needs surgery he could be out for the rest of this season and possibly all of next year.
''I don't think it's anything you want to rush into,'' the manager said.
The Angels' rotation was the team's deepest area just six weeks ago, but four potential starters are sidelined in various stages of recovery from arm injuries. Los Angeles already is without injured left-handers Andrew Heaney and C.J. Wilson, while Tyler Skaggs still hasn't returned from his own elbow ligament replacement surgery in August 2014.
The Angels could use a fifth starter and a source told The Associated Press on Monday that the team is close to a deal with two-time Cy Young Award winner Tim Lincecum, a free agent coming off hip surgery.