"It flared up here and there," Rasmus said, "but recently it was a little more than it has been in the past so I just figured I'd get it fixed and move on from there."
Rasmus will have the surgery Tuesday in Tempe. He can activate his arm in the next three to four weeks, "but certainly nothing aggressive for six weeks," Scioscia said. That would make him unavailable until at least early May.
Rasmus, acquired from the Braves for Scott Downs in July 2013, posted a 2.57 ERA and a 1.05 WHIP in 30 appearances for the Angels last year, striking out 9.2 batters per nine innings. The 27-year-old right-hander was especially crucial in September, providing multiple innings during bullpen games whenever Garrett Richards' turn came up.
"It's always frustrating to have a setback here and there," Rasmus said, "but in the grand scheme of things, it's something that will be taken care of pretty quickly, hopefully, and I'll be back out pitching in no time."
Two bullpen spots now appear open, though Vinnie Pestano looks like a strong fit for one of them. The only other relievers left in camp -- besides mainstays Huston Street, Joe Smith, Fernando Salas, Mike Morin and Cesar Ramos -- are Matt Lindstrom, Ryan Mattheus, Cam Bedrosian and Scott Snodgress. Lindstrom is an XX(B) free agent, which means he can opt out of his Minor League contract if not on the Opening Day roster. Mattheus also signed a Minor League deal, but once placed on the active roster, he must slip through waivers in order to be optioned back to the Minors.
Scioscia mentioned starters Drew Rucinski and Jose Alvarez as candidates to provide length out of the bullpen, which would keep Ramos in the role of a quasi-lefty specialist. The Angels also have local product Adam Wilk, a lefty starter who can potentially provide length out of the bullpen if they need it.
"It definitely opens up a void," Scioscia said of Rasmus' injury. "Cory was a guy that we felt pitched in a variety of roles for us last year, and I think he gained a lot of confidence from just getting those starts at the end of the season. We have some good arms. I think the depth is there. Obviously it'll take one guy out of the picture in the short term."
Alden Gonzalez is a reporter for MLB.com. Read his blog, Gonzo and "The Show", and follow him on Twitter @Alden_Gonzalez. This story was not subject to the approval of Major League Baseball or its clubs.