UFC lightweight champion Anthony Pettis injured his knee and is out of his title defense against Josh Thomson in Sacramento on Dec. 14.
Pettis, who submitted Benson Henderson earlier this year to win the lightweight championship, was supposed to make his first title defense against Thomson, the scrappy former Strikeforce lightweight champion.
The announcement came Sunday night from UFC President Dana White.
The new main event for the UFC on FOX card will be UFC flyweight champion Demetrious Johnson battling Joseph Benavidez. That fight was originally scheduled to take place as part of The Ultimate Fighter Season 18 finale.
Nate Diaz vs. Gray Maynard will now be moved up into the main event of that card on Nov. 30.
White did not disclose any details of Pettis’ knee injury. The Milwaukee, Wisconsin fighter has a history of knee problems.
Thomson, who fought three epic battles against Gilbert Melendez in Strikeforce, is coming off a KO victory over Nick Diaz.