Collison rolled his ankle in the fourth quarter of the Thunder's 123-115 win over the Hawks on Friday. Following the game, Collison needed crutches to exit the arena, and had a walking boot on.
"I don't feel good," Collison said following the game. "Usually I know whether I can play [on it] or not, and I knew I couldn't play after I rolled my ankle."
A 10-day absence would have Collison missing at least five games, which is another blow to the already injury-depleted Thunder, who are dealing with possible season-ending ailments to both Kevin Durant and Serge Ibaka.
"There's that saying, if you don't laugh, you're gonna cry," Brooks told reporters. "And sometimes I feel like crying."
Collison was the final remaining player on the Thunder's training camp roster that hadn't missed a game due to injury this season. He had one of his best games of the season Friday against the Hawks, scoring 13 points with five rebounds, and two important blocks in the second half.
Collison, 34, is averaging 4.1 points and 3.7 rebounds in 16.2 minutes per game.
The Thunder (39-30) currently hold a two-game lead over the New Orleans Pelicans for the West's eighth seed.