What's ailing Brock Lesnar?

Brock Lesnar and Frank MirJon Kopaloff/Getty Images

Mononucleosis managed to do what no fighter could so far: Take out Brock Lesnar.

Being physically fit is expected to protect you from the ailments of the paunchy, malnourished fast-fooders.

Brock Lesnar, who looks like he could gore a bull with his bare hands, does not fit the profile of someone who has to think about the sniffles.

Yet here he is, via trainer Greg Nelson, floating the idea that the illness keeping him from a Nov. 21 date with Shane Carwin is likely to cost him a Jan. 2 booking -- and beyond.

"I'm not sure exactly what it is he has, mono or whatever, but I know that he was sick and couldn't get a good, hard workout in," Nelson told Yahoo's Kevin Iole.

"Mono or whatever" isn't terribly specific, but according to Dave Meltzer, Lesnar was more concise to his employers, informing Dana White on Wednesday that he contracted the mononucleosis virus. The repercussions could be considerable: Mono in adults can linger for months after the initial onset, and prolonged fatigue is not uncommon. I came down with it at 17, and it was -- next to some ProElite telecasts -- one of the worst experiences of my life. Mono doesn't settle in for a week and then disappear. It squats in your cells for a good, long time and it's fond of flaring during physically or mentally arduous stretches in your life.

Lesnar may have contracted it by drinking from someone else's glass, getting coughed on or kissing someone. (You can float that last one by him. I'll wait here.) Alternately, he may have had it when he was younger and it's re-activating.

At best, it will dial down Lesnar's training to embers for the next couple of months. At worst, he'll never be the same fighter again. And that's no exaggeration.