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04/27/11 7:17 PM ET

Thatcher slated for left shoulder surgery

SAN DIEGO -- Padres left-handed reliever Joe Thatcher will undergo exploratory surgery Monday that will determine if he can pitch again this season.

Thatcher said Wednesday that Padres doctor Heinz Hoenecke will perform surgery on his ailing left shoulder, one that sidelined him in Spring Training and hasn't improved nearly enough since with rehabilitation and a throwing program.

Thatcher said Hoenecke won't know the severity of the damage to the shoulder until the surgery occurs.

"If it's just a cleanup, shaving of the labrum, then I could be back by August," Thatcher said after the Padres lost to the Braves, 7-0. "If it's a repair, then we're looking at nine to 12 months."

Thatcher complained of pain in the shoulder while he was throwing a bullpen session Tuesday, marking the second time this month that he's had to stop a bullpen session due to discomfort in his shoulder.

Thatcher, who in 2010 was one of the top left-handed specialists in the National League, was sidelined early in Spring Training and never appeared in a Cactus League game.

Thatcher went through similar shoulder trouble last Spring Training and started the season on the disabled list. But the shoulder responded well to treatment and he was able to rejoin the Padres in mid-April.

He began the season on the disabled list with the hope he would be ready to start a Minor League rehabilitation stint sometime this month.

But Thatcher couldn't get past the pain he twice encountered in his bullpen sessions.

"It's been a long and frustrating two months," Thatcher said.

Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.