The team announced Friday that Westbrook would need the surgery to repair cartilage in his right knee and that he would be out indefinitely.
Westbrook, who has a lateral meniscus tear in his right knee, was hurt when rookie Patrick Beverley tried for a steal in the second quarter of Game 2 and ran into his knee.
Brooks also said on Saturday at the team's shootaround that Reggie Jackson would start for Westbrook later in the evening in Game 3 of the best-of-seven series, which the Thunder lead 2-0.
It will be the first time Westbrook has missed a game in his career. He has appeared in an NBA-best 394 consecutive regular-season games and each of Oklahoma City's 45 playoff games.