Texas Rangers pitcher Neftali Feliz needs Tommy John surgery to repair a tear in his right elbow and likely will be sidelined until next summer.

The two-time AL champion Rangers said Feliz will have surgery on Wednesday. On Tuesday, the AL West leaders acquired ace Ryan Dempster from the Chicago Cubs.

Feliz was 3-1 with a 3.16 ERA in eight games, including seven starts. He has been on the disabled list since May when he was diagnosed with a ligament sprain in his elbow.

"It's a blow for him and for the club," Rangers general manager Jon Daniels said. "We all felt like he was making strides as a starter.

"It'll be a challenge for him, but the nature of the injury, guys do come back. The success rates are high," he said.

Feliz appeared to be on the mend after making three rehabilitation starts with Triple-A Round Rock. But he was scratched before a scheduled fourth start Sunday because of elbow discomfort.

Feliz was the Texas closer last October and was one strike away from clinching the Rangers' first World Series championship before the St. Louis Cardinals rallied in Game 6. The Cardinals won the championship the next day.