Oklahoma City Thunder guard Russell Westbrook had arthroscopic knee surgery on Friday and will be sidelined until after the all-star break.
Westbrook will miss at least 27 games.
General manager Sam Presti said in a news release earlier in the day that Westbrook has been playing pain-free, but "recently had experienced increased swelling" in his right knee.
Coach Scott Brooks said Reggie Jackson, who is averaging 12.5 points, will start. Jeremy Lamb will also see increased playing time in Westbrook's absence.
Westbrook's knee problems began in April when he tore his meniscus in the second game of the Western Conference playoffs, sidelining him for the remainder of the postseason.
He had a second arthroscopic surgery as the Thunder were preparing for training camp after developing inflammation in the knee. However, Westbrook missed only two regular-season games before returning to the floor.
Oklahoma City has since gone on a 21-3 tear with Westbrook in the starting lineup. The five-year NBA player is averaging 21.3 points, seven assists and six rebounds.
Al Horford, the Atlanta Hawks' leading scorer and rebounder, is out indefinitely with a torn right pectoral muscle.
Carmelo Anthony will likely miss both ends of the New York Knicks' series with the Toronto Raptors because of a sprained left ankle.
The NBA has fined Memphis Grizzlies forward Zach Randolph $25,000 for publicly criticizing officials after Memphis lost, 100-92, in Houston.
Randolph was unhappy Thursday night that James Harden, who was 2 for 9 from the floor, went to the free-throw line 25 times. Harden was 9 of 11 at the line in the fourth quarter and became the first player ever to register 27 points on two or fewer field goals.
Randolph was given a technical late in the game.
After, Randolph said the officials made the matchup eight-against-five and dictated the game with what he called "horrible refereeing."
Portland's LaMarcus Aldridge, who had 32 points and 10 rebounds for the Trail Blazers in a 116-112 overtime win over the Los Angeles Clippers Thursday night - his first game after having his wisdom teeth out: "I've had nothing but soup for the last four days, so I was a little worried about my energy levels."