Georges St-Pierre typically is unflappable.
St-Pierre, the Ultimate Fighting Championship's welterweight champion since December 2007, is the consummate gentleman in public and in interviews. St-Pierre rarely has a cross word for an opponent and avoids the prefight insults of most contemporaries.
Last Saturday, however, St-Pierre reached his breaking point.
Following his win over B.J. Penn, welterweight contender and former Strikeforce champion Nick Diaz questioned the validity of St-Pierre's recent knee injury that caused him to withdraw from a title defense against Carlos Condit.
"I don't think Georges is hurt," Diaz said. "I think he's scared. I think he's scared to fight everybody right now."
According to UFC President Dana White, the remark set St-Pierre off backstage.
"I've known Georges St-Pierre since 2004, and he's one of the nicest guys I've ever met," White said. "He's exactly the same no matter what the situation is, no matter who he's fighting. Since 2004, I've never seen him like he was tonight. Georges St-Pierre flipped out tonight after Nick Diaz was in the ring."
White said St-Pierre called Diaz "the most disrespectful human being I've ever met" and promised to "put the worst beating you've ever seen on him in the UFC."
The upheaval resulted in a change to the welterweight-title picture. Diaz vaulted over Condit, who was expected to fight St-Pierre next, and will fight for the title in February. Condit will get his shot if he wins one more fight.
"You've got to come off like that just to get a fight," Diaz said. "I've got to be the bad guy. You point your finger and make me the bad guy. I'm the bad guy now, and now I get a fight."
Diaz was originally slated to face St-Pierre last weekend, but the title shot was stripped from him after he failed to make several scheduled media appearances.
"I don't want Nick not to be Nick, but I want him to play the game a little bit," White said. "We had a little bumpy start, but we'll how this ride goes from here on out."
Middleweights Chris Leben and Mark Munoz meet in the main event of "UFC 138" on Saturday. The card, which will be held at the LG Arena in Birmingham, England, will air on tape delay on Spike TV at 8 p.m. EDT.
The remainder of the televised card includes (bantamweight) Brad Pickett vs. Renan Barao; (welterweight) Thiago Alves vs. Papy Abedi; and (lightweight) Terry Etim vs. Edward Faaloloto and Paul Taylor vs. Anthony Njokuani.
The preliminaries, which air on www.facebook.com/UFC live at 12:50 p.m., include: (light heavyweight) Cyrille Diabate vs. Anthony Perosh; (welterweight) John Maguire vs. Justin Edwards; (featherweight) Michihiro Omigawa vs. Jason Young; (heavyweight) Rob Broughton vs. Philip De Fries; (welterweight) Chris Cope vs. Che Mills; and (bantamweight) Chris Cariaso vs. Vaughan Lee.
The UFC saw two of its popular fighters announce their retirement following losses at "UFC 137."
Penn, whose left eye was nearly swollen shut and who suffered multiple cuts during the fight with Diaz, caught announcer Joe Rogan by surprise.
"Joe, this is probably the last time you're ever going to see me in here," Penn, 32, said. "I want to perform at the top level. That's it, Joe. I'll shake your hand right now."
Rogan asked for clarification from Penn, who competed in 11 title fights among his 21 appearances in the UFC.
"You know what, I've got a daughter at home and another daughter on the way," he said. "I don't want to go home looking like this. I'm done."
And Mirko "Cro Cop" Filipovic retired after his loss to Roy Nelson. Filipovic, who started his career in Japan and won the PRIDE 2006 Open-Weight grand prix, finished his career with a 27-10-2 record with a no-contest.
ProElite debuts its first live card on HDNet on Saturday with former two-time UFC heavyweight champions Tim Sylvia and Andrei Arlovski in co-main events. Sylvia will face Andreas Kraniotakes and Arlovski will face Travis Fulton.
The event will also feature the quarterfinals of the promotion's heavyweight tournament. The eight-man field features Mark Ellis vs. Ryan Martinez, Justin Frazier vs. Jason Bosler, Jake Heun vs. Ed Carpenter and Richard Odoms vs. Rocky Overstreet.
The preliminaries include (welterweight) Reagan Penn vs. Evan Cutts, (lightweight) Waylon Lowe vs. Floyd Hodges and a heavyweight tournament reserve bout between Todd Monaghan and Richard McCraw.
The card, which will be held at the I Wireless Center in Moline, Ill., airs live on HDNet at 7 p.m.