The Thunder announced the injury Friday and said Westbrook would have surgery "in the coming days.'' The team did not give a timeline for his return.
Westbrook was hurt in Game 2 of the Thunder's playoff series against Houston on Wednesday night. Rookie Patrick Beverley lunged into him trying for a steal in the second quarter and his hip collided with Westbrook's knee.
Westbrook, who is in his fifth season in the NBA, has never previously missed a game. He had the league's longest active streak of consecutive games played, with 394 straight regular-season games. The All-Star has played in all 45 of Oklahoma City's playoff games.
Game 3 of the playoff series is Saturday night in Houston.
Westbrook averaged 24 points and seven assists in the first two games, both won by Oklahoma City. Westbrook remained in the game Wednesday night, but was clearly hobbling after the injury. He sat out the Thunder's practice on Thursday, and coach Scott Brooks claimed he would be "fine tomorrow.''
"Our players' health is our first and foremost concern. The Thunder's medical team and several specialists we consulted with determined that Russell undergo a procedure to address the issue,'' Thunder general manager Sam Presti said in a statement.
"We have thoroughly discussed this with Russell. Despite being the competitor and teammate that he is, he respects and understands the decision and is committed to come back even stronger. Certainly Russell is a leader and core player for this team, but we are in the midst of the playoffs and I know other players are determined to step up and contribute.
"We have a resilient group of players who have always taken pride in playing as a team and that approach will continue.''