The Mavs, who have won two in a row against NBA bottom-feeders Washington and Charlotte after their 2-7 start after the All-Star break, begin a stretch Saturday of 10 consecutive games against teams currently holding down playoff spots.
Marion has played through the soreness until now, saying prior to the game that he needed to sit this one out. He was the only Maverick to have played in all 45 games prior to Saturday.
"It's not any worse, but the thing is, it isn't getting better," Marion said prior to the game. "There's a lot of discomfort. It makes me conscious of everything I'm doing."
Marion, the Mavs' top perimeter defender who has been charged with guarding not only the league's best wing players, but often the top point guards since Delonte West fractured his finger in mid-February, has complained of being worn down since prior to the All-Star break.
Mavs coach Rick Carlisle said the injury is not considered serious, but said it's something that must be corrected. Dallas faces the stiffest home stretch in the NBA, as it faces 15 playoff teams in its final 21 games.
They'll take on the Spurs without starting center Brendan Haywood, who sprained his right knee Thursday against Charlotte in his second game after missing four games with a sprained right ankle.
West had the pins removed from his right ring finger on Friday, but the team still has no timetable for his return.
Marion is the Mavs' third-leading scorer at 11.2 points and is tied for the team lead at 6.8 rebounds while averaging 30.7 minutes. He has been invaluable on the defense end guarding up to three positions in any given game.
"That's worn him down," owner Mark Cuban said. "It's worn everybody down trying to compensate for other guys. It's just a weird season."