The 29-year-old American, a two-time NBA scoring champion and seven-time NBA All-Star, will be re-evaluated in about four weeks - or less than a week before the Thunder visits defending champion Golden State for an October 16 opening-night game.
The team says Westbrook decided after suffering from inflammation in the knee this past weekend that he'd have the procedure.
The operation was performed by Neal ElAttrache in Los Angeles with Thunder medical personnel present.
The Oklahoma City Thunder will likely be missing their star guard and former Kia MVP victor when they open camp in less than two weeks. Training camp is scheduled to begin on September 25.
Following a collision with Patrick Beverley in the 2013 playoffs that resulted in a meniscus tear in his right knee, Westbrook underwent three surgeries on the knee in a nine-month span.
The Thunder are saying it's just "maintenance", but this has to put a scare into Oklahoma City fans.
The 2016-17 MVP is coming off the second straight season in which he averaged a triple double and the first season he led the National Basketball Association in assists. He started in all 67 games he appeared in for the Atlanta Hawks last season, averaging 19.4 points and 6.2 assists per game. In 10 National Basketball Association campaigns, all with the Thunder, he has averaged 23.0 points, 6.6 rebounds and 8.2 assists a game.