The GM announced Westbrook went under the knife to repair a torn lateral meniscus in his right knee.
Westbrook suffered a meniscus tear in his right knee Wednesday during the second quarter of the Thunder's win over Houston in Game 2 of their Western Conference quarterfinal series.
He was originally listed as out indefinitely after suffering the injury.
"Although we are of course disappointed that Russell will be unable to return to the floor with his teammates this season, the opportunity to repair the meniscus as opposed to remove it was the best possible scenario for Russell's long term health as a player and person," Presti said.
The Thunder hold a 2-0 lead over Houston in the opening-round series, with Game 3 set for Saturday in Houston.
Westbrook, in his fifth NBA season, averaged 23.3 points a game during the regular season. He scored 29 points while playing 37 minutes during the game in which he was injured.
He combined with fellow superstar Kevin Durant to carry Oklahoma City into the NBA Finals last season.