Los Angeles Angels right-hander Garrett Richards has a torn ulnar collateral ligament in his throwing elbow is expected to have season-ending Tommy John surgery, Yahoo Sports first reported Friday.

Source: Angels ace Garrett Richards has torn ulnar collateral ligament and is expected to need Tommy John surgery. https://t.co/wkbiUpTCl0

— Jeff Passan (@JeffPassan) May 6, 2016

Source confirms: #Angels' Richards needs Tommy John surgery. First reported: @JeffPassan.

— Ken Rosenthal (@Ken_Rosenthal) May 6, 2016

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Richards, 27, is 1-3 with a 2.34 ERA and 34 strikeouts in six starts (34 2/3 innings) this season. He set career highs in wins (15), strikeouts (176) and innings pitched (207 1/3) in 2015.

On Thursday, the Angels announced Richards would miss his scheduled start Friday because of dehydration and fatigue. But the problem turned out to be much more severe.

His loss is a big blow to the Angels, whose rotation ranks 17th in the majors with a 4.45 ERA. Los Angeles is 13-15 and four games behind the AL West-leading Seattle Mariners.

In six major-league seasons, Richards is 40-32 with a 3.58 ERA.