Looper, 36, was a candidate for the Cubs' fifth spot in the rotation, which has not been finalized. He pitched two innings in relief on Thursday against the White Sox and appeared in five games, posting a 9.95 ERA. Carlos Silva, Andrew Cashner and Casey Coleman are competing for the opening.
Looper did not pitch last season after going 14-7 with a 5.22 ERA with the Brewers in 2009. He compiled a career 72-65 record, 103 saves and 4.15 ERA in 670 games with the Cardinals, Marlins, Mets and Brewers.
"After taking the year off, he came in and gave it a good shot," Cubs general manager Jim Hendry said. "We just felt in the end he wasn't going to be able to break with the 12 [pitchers].
2010 Spring Training - null
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"He certainly had an outstanding career and it was a good, sound idea and I'm glad we did it," Hendry said about inviting Looper to camp. "He handled himself like a true professional and was very helpful to the young pitchers in camp and was very appreciative of the opportunity and understood why he could not break with the 12."
Looper lives in the Chicago area and had said at the start of camp that he didn't want to pitch anywhere except with the Cubs because he didn't want to relocate his family again.
"Here's a guy like this who has over 11 years in the big leagues, he's taking another shot, kind of a local guy in the Chicago area," Cubs manager Mike Quade said. "He came in and gave it everything he has. You feel bad, but he had a wonderful career. He's got a good family. He's got a lot going for him. I've let people go in the past who didn't have the personal qualities that Loop has ... and it was tough to send him out.
"He'll be just fine. My sense is, given the way he handles himself, when the kids are gone and he wants to come back in the game, he needs a recommendation, he can call me."