UFC 151 has been called off after Dan Henderson, one of the fighters in the main event, discovered a partial tear to the medial collateral ligament in his right knee. The UFC 151 card was slated for Sept. 1 at the Mandalay Bay Events Center.

UFC president Dana White said light heavyweight champion Jon Jones, the other main event fighter, declined to fight Chael Sonnen who White proposed  as a replacement for Henderson.

"I'm stunned," White said. "We've never had a situation where this happened before, where a champion wouldn't step up to fight."

Jones agreed to fight Lyoto Machida on Sept. 22 at UFC 152 in Toronto. It is a rematch of the main event of UFC 140, which Jones won by choking out Machida in the second round.

White had nothing but high praise for Sonnen for being willing to take on a fight on such short notice.

"Chael's been out there talking all this crazy [expletive] about Jones, but he proved that he not only talks the talk, he walks the walk," White said. "I offered the fight to a couple of guys, and believe me when I tell you, nobody wants to fight Jon Jones on [short] notice. Nobody. But when I called Chael, that crazy [expletive] said, 'Not only will I fight him, but I'll get on a plane and fight him at Mandalay Bay tonight, if that's what you want.' "

White said the decision to cancel the show was the first time in more than 11 years owning the UFC he had to do that. The UFC canceled a planned March show in Montreal, but that was before matches were officially announced.