BOSTON (AP) – Red Sox third baseman Bill Mueller had arthroscopic surgery on his right knee to remove a “hanging piece of cartilage” on Friday before returning home to recuperate.

The defending AL batting champion is expected to miss five-to-six weeks.

Manager Terry Francona declined to speculate on Mueller’s return, saying, “Those timetables aren’t very good.”

“He had a relatively short procedure,” Francona said before Boston’s game against the Seattle Mariners. “He feels real good about that. I think the doctor feels real good about that.”

Mueller was batting .262 with five homers and 21 RBIs. Last season, he hit .326 to edge teammate Manny Ramirez for the AL batting title by a point.

Mueller’s knee began swelling early this mont. He decided on Tuesday to have surgery and he was placed on the disabled list retroactive to May 20. Dr. David Zeman, who operated on Mueller’s left knee in 2002, performed the surgery.

in Phoenix.

“There was nothing surprising. … There’s no structural damage,” Morgan said. “He’ll start his therapy tomorrow. … Once the swelling goes down, three weeks or so before he starts his baseball activities.”

Mueller is the third injured Boston starter.

Shortstop Nomar Garciaparra (heel) and outfielder Trot Nixon (back, leg) have not played this season. Garciaparra was scheduled to face live pitching on Saturday; if all goes well, the team could develop a plan to get him a rehab assignment next week.

“After he hits tomorrow, (trainer) Chris Correnti and I will get together on a schedule,” Morgan said.

Nixon played an extended spring training game on Thursday and will play in another on Saturday, Francona said.

“His back is feeling very good. His quadricep, mostly, is feeling pretty good,” Morgan said. “He had a little bit of a pull running the bases, not much.”

Rookie Kevin Youkilis has played third since Mueller was sidelined and is hitting .286 with 11 runs and a .447 on-base percentage.

“When Nomar comes back, we’re going to pick and choose,” Francona said. “But he (Youkilis) is going to play a lot.”

Pitchers Byung-Hyun Kim (back) and Scott Williamson (right elbow inflammation) are also hurt. Williamson, who has one save and a 1.69 ERA in 14 relief appearances this season, is still resting his arm, but he will travel to the West Coast with the team.

“The report today is that everyday he feels better and better,” Francona said of Williamson. “He’ll be throwing again pretty soon.”

AP-ES-05-28-04 1821EDT