CHICAGO -- Mark Prior had exploratory arthroscopic surgery on his injured right shoulder Tuesday, and it was unclear how long the Cubs pitcher would be sidelined.
The team had no immediate information on the procedure, performed by Dr. James Andrews in Birmingham, Ala., before Chicago's game Tuesday night with the Milwaukee Brewers.
Before the surgery, Cubs general manager Jim Hendry said he wasn't sure if Andrews would have to fix anything in Prior's shoulder, which has been giving the right-hander problems since last season.
Prior has been battling injuries since his first full season in the majors in 2003 and he was not on the Cubs' active roster to start the year. He was optioned to Triple-A Iowa after a poor spring training, but instead went to extended spring training in Arizona. He pitched two innings there April 12 before reporting discomfort in his shoulder.
Prior went to Dr. Lewis Yocum in California before going to see Andrews, who told Prior last October he had genetic looseness in his shoulder joints.
Prior, 26, is 42-29 with a 3.51 ERA in his career. He made just nine starts last year after three trips to the disabled list and took a slight pay cut this season, from $3.65 million to $3.575 million. Prior finished third in NL Cy Young voting in 2003, when he 18-6 with a 4.24 ERA and struck out 245 in 211 1/3 innings.