Garrett Richards will be out six to nine months after an MRI showed he suffered a torn left patellar tendon, the Los Angeles Angels have announced.

"You're going to be thinking of Garrett once every fifth day when he was out there," Mike Scioscia said. "You might not be able to replace that, but it doesn't mean that we're not going to be able to reach our goal as a cumulative pitching staff."

Richards is scheduled to undergo surgery Friday.

He sustained the injury Wednesday night against the Boston Red Sox while covering first base in the second inning.

The Angels are 19-7 when Richards starts this season, but just 56-43 when anyone else does.