The Wizards say Thomas will be sidelined indefinitely and will be re-evaluated in two weeks. He was injured in the first quarter of Monday night's 97-91 loss to the Milwaukee Bucks.
Thomas missed all of last season while recovering from open heart surgery. He was expected to move back into the starting spot after Haywood tore a wrist ligament during preseason. Instead, Thomas has been on and off the bench, playing in 26 of 37 games with seven starts.
Arenas has yet to play this season after knee surgery in September, and Haywood might not return at all this season. Stevenson has been sidelined for two weeks with a bad back.