AUBURN HILLS, Mich. -- Ben Wallace could miss the start of the playoffs for the Detroit Pistons with a left knee injury.

	Wallace

Wallace, who leads the NBA in rebounding and blocked shots, is expected to be sidelined for two weeks after an MRI exam Monday showed he has a sprained medial collateral ligament.

The Pistons (47-29) lead the Central Division and have clinched a berth in the playoffs, which start April 19. Detroit has six games left in the regular season, including Tuesday at Philadelphia.

Wallace was injured Sunday against San Antonio, when teammate Tayshaun Prince fell backward into him on defense. Wallace went down and had to be helped off the court.

"From the way it felt and sounded when I hit him, I thought he was going to be out for a long time," Prince said.

Wallace wouldn't comment when reached at home Monday.

The 6-foot-9, 240-pound Wallace became the first undrafted player to be voted as an All-Star starter this season. He played in the All-Star Game one day after his mother's funeral in Alabama.

Wallace is averaging 6.9 points, 15.4 rebounds and 3.15 blocks. He's on pace to become the first player in NBA history to top the league in each of the latter two categories twice. Last season, he joined Kareem Abdul-Jabbar, Bill Walton and Hakeem Olajuwon as the only players to lead in rebounds and blocks.

Wallace, who plays a team-high 39.4 minutes a game, has helped Detroit's defense hold opponents to a league-low average of 87 points.

The Pistons had the Eastern Conference's best record from March 8 until Sunday night, when they lost their third straight game and fell a half-game behind New Jersey. Detroit's lead over Indiana in the Central Division has dwindled to 1½ games.

"You hate to see anyone go down, but we can't panic," forward Cliff Robinson said. "We've just got to keep playing."

Meanwhile, Pistons coach Rick Carlisle said the team expects to activate Zeljko Rebraca on Monday. The center has been on the injured list since Jan. 6 because of an irregular heartbeat.

Detroit also was without point guard Chauncey Billups, its second-leading scorer, against the Spurs. Billups sat out due to a sprained ankle and said his status is day-to-day.

Wallace finished with 10 rebounds and two blocks. He left the arena on crutches.