ARLINGTON -- Rangers infielder Hank Blalock underwent surgery on Friday to relieve the pain and discomfort of Carpal Tunnel Syndrome in his right wrist and is expected to be sidelined at least four more weeks.

The operation -- known as Carpal Tunnel Release Surgery -- was performed by Dr. Tom Diliberti in Dallas. CT is caused by inflamed tendons putting pressure on the nerves in the wrist and the operation is designed to relieve that pressure.

Blalock was already on the disabled list with a partially torn hamstring and was supposed to be activated next week. He was also supposed to move to first base. But he developed CT while working out in Arizona and needed an injection to relieve the pain.

The Rangers were hoping the injection would take care of the problem, but Blalock did not respond quickly to it and decided to have the surgery.

"Right now, the sense is it will be 10 days before the incision is healed," Rangers general manager Jon Daniels said. "Shortly after that he'll begin baseball activities and it sounds like it will be three to four weeks until he can get out there again."

Daniels said the plan is still for Blalock to switch to first base when he is ready to play baseball again.

"This has no effect on that," Daniels said. "It's also a less demanding physical position, especially on the right arm."

Blalock, a two-time All-Star in 2003-04, was placed on the disabled list on April 29 after hitting .299 with three home runs and seven RBIs in 22 games.

"We were certainly looking forward to getting his bat back in the lineup," Rangers manager Ron Washington said. "Anytime you can add an experienced bat like Hank's back in there and his gamesmanship, it would certainly help."

Instead, the Rangers will continue to platoon Frank Catalanotto and Chris Shelton at first base. Ramon Vazquez has taken over at third base and the Rangers called up Travis Metcalf from Triple-A Oklahoma on Friday to replace German Duran as his potential platoon partner.

Metcalf started the year on the DL after tearing his hamstring in Spring Training. The Rangers activated him on May 8 without a rehab assignment because they needed a backup infielder. He was 0-for-1 during his week with the Rangers before being sent to Oklahoma. He batted .238 with three doubles and eight RBIs in 11 games for the RedHawks.

"I went down to get the leg healthy and that's what's happened," Metcalf said. "The leg feels fine. I don't know if there's any residual effect but I've had no pain."