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05/12/08 9:48 PM ET

Prior takes step back in rehab

Shoulder discomfort during throwing session prompts MRI

CHICAGO -- After suffering a previously reported setback in his rehab program this weekend, pitcher Mark Prior was scheduled for an MRI on his right shoulder Monday, Padres manager Bud Black said.

"Mark was throwing on the side, getting ready for batting practice, a couple days ago and felt quite a bit of discomfort in his shoulder, and he shut down his throwing session and came back to San Diego," Black said.

After meeting with Padres doctors Monday, there's a chance Prior will take that familiar trip to Birmingham, Ala., on Wednesday, to see Dr. James Andrews, who performed arthoscopic surgery on his nettlesome shoulder on April 24, 2007. Prior was shut down for eight days in April because of soreness.

"Mark had been on a nice path," Black said. "He had to take a step back a couple weeks ago, but I think you can probably deem this a setback for sure."

The Padres signed the oft-injured 27-year-old to a one-year deal a day after Christmas knowing he would take some time to recover from the surgery. He threw off a mound for the first time in late March, and there hadn't been a firm timetable for his return.

Jon Greenberg is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.