A partial tear to the medial collateral ligament in Dan Henderson's right knee forced the cancellation Thursday of the entire UFC 151 card, which was slated for Sept. 1 at the Mandalay Bay Events Center.

UFC president Dana White said light heavyweight champion Jon Jones declined to fight Chael Sonnen, whom he proposed as a replacement for Henderson. That would have kept the show alive, but White said when Jones wouldn't agree to meet Sonnen, he had no choice but to cancel the show.

"I'm stunned," White told Yahoo! Sports on Thursday. "We've never had a situation where this happened before, where a champion wouldn't step up to fight."

Jon Jones was in attendance at UFC 148 when Anderson Silva beat Chael Sonnen. (Getty) More

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 heaped praise upon Sonnen for being willing to take the 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.' "

Henderson said Thursday he injured his knee while defending a takedown in practice. He said it won't require surgery, but doctors advised him to stay completely off of it for three weeks. He said the knee "is pretty unstable right now."

He was devastated by the cancellation because he believed he had a great opportunity to upset the highly regarded Jones, who is rated No. 2 in the world in the Yahoo! Sports pound-for-pound rankings. He said he was willing to fight injured if he had any way of doing so, but said the lack of stability in his knee prevented that.

"This is the first time in UFC history that the champion wouldn't step up and fight [a replacement], and I was pretty shocked to hear that," Henderson said. "It's not like he's injured. It's unbelievable to me that he wouldn't take that 'the show must go on' attitude. If there was any way I could have gone, and any way that I thought I could give myself a chance to win, I would have done that."

In a bid to save the card, White called several fighters and offered them the match against Jones. None but Sonnen, though, wanted to take on Jones without the benefit of a full training camp.

Sonnen, a middleweight who announced during an appearance on Fuel TV on Aug. 14 that he would be moving up to light heavyweight for a Dec. 29 fight against Forrest Griffin, was willing to take the risk.

Sonnen, who was knocked out by middleweight champion Anderson Silva after missing a spinning back fist in a highly profitable rematch on July 7 in Las Vegas, said he never considered saying no.

"I was shocked and I'm shocked much more that the show was canceled," Sonnen said. "We all have to pitch in and help. It surprised me [Jones turned down the fight]. That's the first time I can recall that happening."

[Related: Fighters react to cancellation of UFC 151]

Sonnen hadn't trained since he lost to Silva and conceded his weight was high. He declined to say specifically what he weighed on Thursday, but said he would have had a lot of work to do to make the 205-pound limit. However, he insisted he would have made it.

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