"Kyle will remain in camp," assistant general manager Thad Levine said. "We had very productive conversations with Kyle and his agent about the prognosis for him for the future and he wants to stay part of this franchise moving forward. We anticipate him to rehab with us and make an impact with us, just maybe a little bit later than we anticipated."
The injury was announced four days after McClellan threw two scoreless innings against the Brewers on Tuesday. It was McClellan's first appearance in a Cactus League game this spring after he was sidelined for three weeks with soreness in the back of his right shoulder.
"When a guy is coming back from shoulder surgery and there is an injury, I think the first cause for concern is if there is any structural issues related to the injury he suffered before," Levine said. "I think that is somewhat the silver lining in this, that the MRI revealed no structural damage. It's truly just a strain."
McClellan spent the past five years with the Cardinals, but his 2012 season was cut short by injury. He went on the disabled list on May 17 with a sore right elbow. While he was on the disabled list, doctors determined that the elbow problem was caused by a damaged shoulder capsule. He underwent surgery on July 10.
McClellan came into camp feeling strong, but developed muscle soreness in the back of the shoulder after his first two live batting practice sessions. He was shut down and did not appear in a game until Tuesday against the Brewers.
McClellan was supposed to start against the Mariners on Sunday in Peoria, but will be replaced by Michael Kirkman.
"There are now opportunities for other people to step up, whether that's in the rotation for the fifth spot or in the bullpen, there is a chance for someone," Levine said.
T.R. Sullivan is a reporter for MLB.com. Read his blog, Postcards from Elysian Fields, and follow him on Twitter @Sullivan_Ranger. This story was not subject to the approval of Major League Baseball or its clubs.