SAN ANTONIO (AP) Tim Duncan was scheduled for a medical exam Friday to determine the extent of his thigh injury.

San Antonio coach Gregg Popovich said after practice that Duncan did not have much swelling in his left thigh. But aside from that he didn't know how bad the injury might be or how many games he might miss.

The NBA's two-time MVP did not practice Friday and he did not speak to reporters.

The Spurs released guard Ron Mercer but did not immediately fill his roster spot. Among the players who could come off the injured list is 6-foot-10 forward Sean Marks, who has not yet played this season.

Duncan hobbled to the bench midway through the third quarter of the Spurs' 115-91 loss to Dallas on Thursday night. At the time, San Antonio trailed by nine points before going on to its most lopsided loss of the season.

In 25 minutes, Duncan scored 22 points and had 17 rebounds. After the game his only comment was, ``I don't know what happened.''

Teammate Malik Rose said he and other Spurs are prepared to step up if Duncan has to sit out to recuperate.

``Tim's one of the toughest guys in the league,'' said Rose, who got some of Duncan's minutes Thursday and finished with 12 points. ``He won't miss much time, but in the meantime we have to be a collective Band-Aid for him.''

San Antonio hosts Denver on Saturday, the start of a four-game homestand that ends with a rematch against Dallas on March 5.

Mercer, a proven scorer, was acquired in an offseason trade but used sparingly. Popovich said the release would allow him to catch on with another team before March 1, the deadline for eligibility for the playoffs.

Mercer played in 39 games this season, averaging 5.0 points and 1.3 rebounds in 13 minutes. He was acquired from Indiana in a three-way trade in July that also involved Sacramento. The Spurs obtained guard Hedo Turkoglu, now a starter, in the same deal.