Juan Gutierrez was unavailable all last week due to a bicep issue, the Orange County Register reports.
The injury may explain some of the Angels' recent bullpen moves, like using starter Jerome Williams in relief last Wednesday. The right-handed reliever is expected to miss at least a few more days.
Gutierrez has a 4.23 ERA and 1.37 WHIP in 44 2/3 innings this season. He's struck out 32 and walked 16.
He joined the Angels on July 24, after being selected off waivers from the Royals, and has a 5.87 ERA and 1.50 WHIP in 15 1/3 innings with Los Angeles.