-- Washington Nationals right-hander Ryan Drese will undergo surgery on his right shoulder in the next 10 days, a procedure that will end his season and leaves the club's rotation thin for the stretch run.

Drese has a tear in the labrum in his right shoulder. The options, General Manager Jim Bowden said, were to have the surgery now, or to try and rehabilitate the injury in hopes Drese would be available for the last 10 days of the season or so. Bowden and Drese discussed the matter by phone Tuesday, and opted for surgery.

"This was affecting his performance," Bowden said.

The Nationals acquired Drese off waivers from Texas in June, and Bowden said he thought an MRI exam taken by the Rangers might have revealed the tear. But Bowden also said "you can't blame the Rangers," and indicated that lots of major league pitchers could be playing through such an injury.

Drese was 3-6 with a 4.98 ERA in 11 starts for Washington, and 7-12 with a 5.78 ERA overall this season. He won 14 games for the Rangers last season, and he is under contract to the Nationals for $1.7 million next season. A sinkerball pitcher, Nationals officials believe the injury prevented Drese from raising his arm high enough to properly throw his best pitch.

The loss of Drese, who last pitched on Aug. 18 in Philadelphia, further depletes the Nationals' rotation. Left-hander John Halama, who made his first start for Washington on Sunday, will take Drese's spot again on Friday against the Phillies, but Manager Frank Robinson said that didn't mean Halama would hold a starting job for the final month of the season.

Right-hander John Patterson, the ace of the staff, left Tuesday's game against the Braves after just 22/3 innings with stomach cramps. Patterson's short outing put the bullpen under a strain headed into Wednesday's doubleheader with Atlanta. Reliever Luis Ayala has been battling elbow tendinitis, and hasn't pitched since Aug. 21.

Right-hander Tony Armas Jr., who has battled shoulder soreness and had to come out of his last start -- Aug. 23 against Cincinnati -- after three innings, is scheduled pitch Thursday in the series finale against the Braves.