CHICAGO -- Chris Carpenter underwent an MRI exam in St. Louis on Thursday, and the test confirmed that the Cardinals right-hander has a tear of the left oblique muscle.
According to general manager John Mozeliak, the official diagnosis does not change the estimated time-table for the 2005 Cy Young Award winner. Manager Tony La Russa estimated on Wednesday that Carpenter would be out for somewhere between four and eight weeks.
Dr. George Paletta, the head team physician for St. Louis, performed the evaluation of Carpenter on Wednesday. Paletta also administered an injection to the injured area. Carpenter sustained the injury on Tuesday during the Cardinals' game against the Diamondbacks in Phoenix.
Carpenter will rest over the weekend and, according to a release from the club, will be re-evaluated next week. At that time he should be able to begin early rehabilitation activities.
Rookie right-hander P.J. Walters gets the first chance to slot into the Cardinals' rotation in Carpenter's absence. Walters will pitch on Friday afternoon against the Cubs at Wrigley Field.
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.