CLEARWATER, Fla. — Philadelphia Phillies closer Brad Lidge is scheduled to have arthroscopic surgery on his right knee tomorrow and could miss the regular-season opener.

Lidge, Philadelphia's biggest offseason acquisition, limped off the field yesterday after injuring his knee when he caught a spike in the mound on his first pitch of batting practice. Doctors removed torn cartilage from the same knee in October.

The 31-year-old right-hander was expected to return to Philadelphia today for surgery tomorrow that would sideline him for three to six weeks. The Phillies open the season at home March 31 against Washington.

Phillies manager Charlie Manuel said setup man Tom Gordon would close if Lidge isn't ready for opening day.

"Ideally, if everything went right I wouldn't miss any of the season because that would be four weeks," Lidge said. "But that will be based on how it feels."

The Phillies acquired Lidge and infielder Eric Bruntlett in a November trade that sent outfielder Michael Bourn, infield prospect Mike Costanzo and reliever Geoff Geary to the Astros. Lidge, who has 123 career saves, finished 2007 with 19 saves in 27 chances and a 3.36 ERA for Houston.

When the Phillies acquired him, it allowed them to strengthen their rotation by making Brett Myers a starter again.

"Right now, if we had to do this during the season, then obviously you're missing a big chunk of the season," Lidge said. "I definitely need a few bullpen sessions, but I feel like my arm is ahead of schedule so after a week I should be able to throw again."

The Phillies struggled with injuries in the bullpen for much of last season. Gordon and Myers both missed significant time.