Marion did not make the trip to Denver where the Mavs will put their three-game win streak on the line with three key players sidelined. Dallas will also be without starting center Brendan Haywood for a second consecutive game with a sprained right knee.
Guard Delonte West remains out with a fractured right ring finger that he injured trying to make a steal in a game against the Nuggets more than a month ago.
Mavericks coach Rick Carlisle told reporters at shootaround in Denver that Marion would have his knee thoroughly examined Monday in Dallas.
"When you've a guy that's played every game and then he misses two games, it's a concern,'' Carlisle said. "We care about him a lot because he's one of our main guys and he's really been one of our warriors all year long. We've got to get to the bottom of it and hopefully we can get him back quickly because we need him. Defensively, he's the best we've got."
Marion considered sitting out last Thursday's game against Charlotte and finally decided he had to rest his knee prior to Saturday's win against the Spurs. Marion, who was the only Mav to play in all 45 games up to that point, said the knee is causing discomfort and that he is concerned because he's not seeing progress.
"It's not any worse, but the thing is, it isn't getting better," Marion said prior to Saturday's game. "There's a lot of discomfort. It makes me conscious of everything I'm doing."
The chronic soreness is especially troubling because Marion has been the team's most consistent player this season as well as being its most valuable defender, often tasked with guarding up to three positions in any given game.
Marion helped to limit Nuggets point guard Ty Lawson to three points and two assists after West left with the broken finger. It started a string of games in which the 6-foot-7 Marion found himself matched up against opposing point guards.
Prior to the All-Star break, Marion complained that the demanding workload was wearing down his body. Since the break, Marion's scoring is down to 8.9 points a game on 40.2 percent shooting.