ANAHEIM ( — Los Angeles Angels left-hander Andrew Heaney will have Tommy John surgery, likely sidelining him until the 2018 season.

The Angels announced the decision Thursday in another blow to the injury-plagued lineup of the AL West’s last-place team.

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Heaney entered the season as Los Angeles’ No. 2 starter after his promising debut for the Angels, who acquired him in a trade in December 2014. He went 6-4 with a 3.49 ERA in 18 starts last season, and was named the AL’s rookie of the month in July.

But Heaney made just one start in April before a tear in his ulnar collateral ligament was discovered. Heaney hoped to avoid surgery with rest and stem cell therapy.

“Based on the lack of progressive UCL healing in Andrew’s case, coupled with discomfort upon testing the ligament while throwing, we have concluded that Tommy John surgery is the necessary course of action,” the Angels announced in a team statement.

Surgeon Neal ElAttrache will perform elbow ligament replacement surgery on Heaney on Friday in Los Angeles.

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Heaney’s long-term absence is among several injury problems for the Angels (32-47), who are on pace for the worst season in franchise history. They have lost nine of 10 heading into the opener of a 10-game road trip on Friday night in Boston.

Angels ace Garrett Richards is attempting to rest a partially torn elbow ligament after making just six starts this season. The right-hander also had stem-cell treatment, but the Angels haven’t determined whether he will be able to avoid surgery.

Richards won 28 games over the previous two seasons for the Angels, who have been without three top starting pitchers for most of the season.

C.J. Wilson hasn’t pitched yet this year due to a series of upper-body injuries, and his recovery prospects are unclear.

The Angels are waiting for the return of touted left-hander Tyler Skaggs, who has been out since August 2014 after Tommy John surgery. Skaggs is currently in the minors, and he hopes to join the Angels in July.

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