WASHINGTON -- Nationals catcher Paul Lo Duca had arthroscopic surgery to repair a torn meniscus in his left knee Monday morning. Lo Duca, who will begin a rehab program later this week, is expected to miss four to six weeks but be ready for Opening Day.

The procedure was by performed by Dr. Benjamin Shaffer, the team's physician and orthopedist, at Sibley Memorial Hospital in the nation's capital.

Lo Duca suffered the knee injury last week while working out in a New York gym. He saw Dr. Andrew Pearle, the Mets' associate team physician, on Friday and had an MRI that revealed the torn meniscus.

Nationals general manager Jim Bowden said Monday afternoon that there isn't any plan to acquire another catcher off the free-agent market in case Lo Duca is not ready to play.

"We think that Paul Lo Duca will be ready by Opening Day," Bowden said. "The doctors repaired a slight tear in the meniscus. Besides that, the joint was completely clean."

Lo Duca, 35, signed a one-year, $5 million deal plus incentives with the Nationals on Dec. 11. He is expected to be the starting catcher and tutor backup Jesus Flores and the young pitching staff.

Lo Duca hit .272 with nine home runs and 54 RBIs for the Mets in 2007.