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07/25/08 11:13 PM ET

Jaramillo undergoes knee surgery

Rangers' hitting coach out of action indefinitely

OAKLAND -- Rangers hitting coach Rudy Jaramillo had left knee replacement surgery in Texas on Friday and will be out of action indefinitely. It's likely he won't be back on a full-time basis until September.

"It's unknown how long he'll be out," assistant general manager Thad Levine said. "When we get back to Texas, we'll sit down with him and see."

Jaramillo has been in severe pain for much of the year, but was hoping to hold off surgery until after the season was over. That wasn't the case.

Minor League hitting coach Mike Boulanger is filling in for Jaramillo during his absence, along with special assistant Johnny Narron.

Triple-A Oklahoma infielder German Duran also had surgery on Friday to repair a torn ligament in his left thumb. He is likely to be out 6-8 weeks. The Rangers are hoping he can make up for lost time by playing winter ball.

T.R. Sullivan is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.