CINCINNATI -- Reds starting pitcher Brandon Claussen will have arthroscopic surgery on his left shoulder and is expected to miss the rest of the season.
On Monday, Claussen decided to have the procedure done after he spent a month on a rehabilitation assignment with Triple-A Louisville. The left-hander has been on the disabled list since June 17 with what was first diagnosed as rotator cuff tendinitis.
Team medical director Dr. Tim Kremchek will perform the surgery, possibly this week. It could take six weeks of rehabilitation before Claussen could resume baseball activities.
"It'll just clean out some of the 'junk' inside his shoulder that a pitcher sometimes gets and won't quite let him get over the hump," Kremchek said Monday night.
An MRI taken in June revealed damage to Claussen's labrum and rotator cuff. He took a cortisone shot and originally opted for rehabilitation.
"I want to get it fixed," Claussen said. "I knew there was a problem there before. Taking a pill is not going to reattach my labrum. I wanted to exercise every option I possibly could before I did it."
In five rehab starts for Louisville, Claussen was 0-2 with an 8.34 ERA and 31 hits allowed over 22 2/3 innings. He also struggled before his injury, going 3-8 with a 6.19 ERA in 14 starts this season for the Reds.
The final day of Claussen's 30-day rehab assignment was Monday. The club would have had to make a roster move on Tuesday if Claussen returned.
"The main thing is for him to have peace of mind and get the surgery done so he'll be ready to go at Spring Training," Reds general manager Wayne Krivsky said. "That's the best thing for him so he can get as much rehab time as possible. We would have liked to have had him available as a starter, but it's not going to happen."
Before this season, Claussen never had any shoulder problems. In 2002, he had Tommy John surgery on his left elbow to repair a torn ulnar collateral ligament.
Mark Sheldon is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.