Starting center Brendan Haywood rolled his left ankle on the first possession of Dallas' game at Oklahoma City on Monday night and went to the locker room.
The Mavericks said Haywood sprained his ankle and his return was questionable.
Dallas won the opening tip and got the ball inside to Haywood, who missed a shot before his left foot came down on top of Thunder center Kendrick Perkins' left foot.
Haywood limped back on defense and fouled Kevin Durant to get the clock stopped so he could leave the court.
The Mavericks were already short-handed with backup center Brandan Wright out while recovering from a concussion.
Sean Williams was called up from the NBA Development League on Sunday to give the team another center on the roster.