Shane Carwin was working out Thursday afternoon at his training camp in Colorado when his cellphone rang. He ignored it, keeping his focus on preparations for his June 11 bout at UFC 131. The phone rang again. And again. "My phone was blowing up," Carwin later wrote on his blog, "so I looked over and saw some missed calls from Dana and Joe Silva."

Carwin sensed the calls were about something important -- UFC president Dana White and the fight organization's matchmaker don't reach out so persistently for no reason -- and he was right. Brock Lesnar, slated to fight Junior dos Santos in the main event of that same pay-per-view card in Vancouver, British Columbia, has had to pull out of the No. 1 heavyweight contender bout because of a relapse of diverticulitis, the intestinal disease that nearly killed him a couple of years ago. With Lesnar out, the UFC brass was calling Carwin to ask if he wanted the dos Santos fight. He did. With a little trepidation but much eagerness.

"Junior is a serious fight and not the type of fight that you would normally take on a 30-day notice," Carwin blogged. "But I have a dream to chase, and I do not have a lot of time to chase it. This is an opportunity to put myself in contention for the title."

Indeed, the winner of the Lesnar-dos Santos bout, which has been heavily promoted during the current season of the Spike reality series The Ultimate Fighter, on which the two heavyweights are serving as team coaches, was promised a shot at champion Cain Velasquez. During a late-afternoon media session announcing Lesnar's withdrawal and the Carwin-dos Santos replacement matchup, White did not specify that the new fight would be for No. 1 contender status. But later, he told Kevin Iole of Yahoo! Sports that that's the case.

Still uncertain is what will become of Jon Olav Einemo, the grappling stud from Norway who was to make his UFC debut against Carwin.

Of course, the bigger question is what will become of Lesnar, who sounded downcast during the UFC conference call as he answered questions about his condition, which might require surgery. The thing the former champion most assuredly wanted to make clear: This was not a retirement announcement.

"This isn't the end of Brock Lesnar," he said. "This is a speed bump in the road, and in my career I've faced lot of speed bumps."

A speed bump? More like a brick wall at the end of a dark alley. A second bout of diverticulitis would be less dire if Lesnar were a fifty-something desk jockey living the easy life, but for an elite athlete -- competing in the most rugged and demanding of all combat sports, no less -- to try to push through a disease so debilitating might be too much to ask of his body. As Lesnar himself acknowledged during the conference call, "I'm not like a lot of people. I consider myself a top-notch elite athlete that has to push his body to other limits, and because of the stress that I've put on my body in training camp, it causes this thing to become active again and not agree with what I'm doing."

So even if Lesnar does return to the Octagon, as he promised, will he ever be the same brute who mowed down everyone in front of him? Lesnar said during Thursday's conference call that he was "85, maybe 90 percent" for last July's bout against Carwin, in which he was knocked down and beaten up in the first round before coming back for a second-round submission win. He didn't put a number on his conditioning for the October fight when Velasquez finished him in the first round to take away the belt, but Lesnar did imply that in that bout he was not the fighter he once was. Moving forward, what will be left?

White seemed to be raising much of the same question when he opened the conference call by saying of Lesnar, "He's got some choices to make in a couple of weeks, whether to fight this thing and continue fighting or not."

White, the UFC's president, has some thinking to do as well. Within a week, the UFC has seen two upcoming main events fall apart, as the UFC 130 rematch between lightweight champ Frankie Edgar and Gray Maynard was postponed Monday after both fighters were injured in training. UFC 131 loses even more star power with the pullout of Lesnar, one of the promotion's most marketable names. He fought just twice last year, yet was the highest paid athlete in MMA, according to an ESPN The Magazine study, bringing in an estimated $5.3 million, much of it his share of pay-per-view revenues. Will people still fork over $55 for the June 11 fights now that Brock won't be there?

Those who do might actually see a vastly more exciting UFC 131 main event than what was the originally planned. Whereas the big question surrounding Lesnar-dos Santos was whether Junior would be able to avoid being smothered beneath a 280-pound Brock blanket and keep the fight standing long enough to knock Lesnar down, dos Santos vs. Carwin is a rock 'em, sock 'em battle of two guys with knockout power and the ability to land it. Although Carwin, like Lesnar, has national championship collegiate wrestling credentials, he's shown a preference to stand and bang. So has Junior. Let's go get referee Herb Dean and announcer Bruce Buffer into the Octagon right now, and let these guys have at it.

Not so fast. The potential stumbling block is one always present when a striker meets a striker: Guys in with someone of their own ilk tend to circle at a distance out of respect, making for a slow start that might or might not evolve into fireworks. Then there's the matter of preparation time, or lack thereof. Each of these 12-1 fighters was training for a ground fight. How well will they enact strategic changes over the next four weeks? And lastly there's the rust to contend with: Dos Santos last fought in August, Carwin in July. Will they be at the top of their game?

They'd better be. One false move could mean instant sleepytime and a lost opportunity to challenge for the UFC heavyweight championship.

Questions? Comments? To reach Jeff Wagenheim or contribute to the MMA mailbag, click on the e-mail link at the top of the page.

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