UPDATE: Coach Rick Carlisle confirmed about an hour before tipoff that Marion is out.
Marion's sore shoulder is feeling better after sitting out Friday night's win over the Sacramento Kings and taking anti-inflammatory medicine, but he's proceeding with caution.
"I just don't want to get out there and it comes immediately back," said Marion, who is averaging 11.1 points and 6.9 rebounds this season. "We're just going to take it slow."
Marion originally bruised the shoulder and his ribs when he crashed to the court during the Mavs' Jan. 7 win over the Los Angeles Lakers. He missed the next four games and played in pain for a couple of weeks before the Mavs decided he should rest the shoulder again.
Dallas is 6-1 when Jae Crowder starts at small forward this season, although coach Rick Carlisle doesn't read much into the Mavs' success with such a small sample size.
"He's done well when he's filled in as a starter this year," Carlisle said of Crowder. "That wasn't the case last year, so that's good. But I'd rather have all our guys available and start Marion and have Crowder off the bench."