What is Brock Lesnar Sick With?

According to UFC President Dana White, Brock Lesnar has a serious illness that will keep him sidelined for the foreseeable future.
He has some kind of disease but they don't say what exactly.
Lesnar's sickness was the reason that the Brock Lesnar-Shane Carwin fight on Nov. 21 was postponed.
What is Lesnar sick with?

Lesnar has reportedly been sick for more than three weeks though his team did not announce the illness is.

UFC president Dana White told reporters today that former WWE star and UFC Hvt. champion Brock Lesnar is "very, very sick" and needs a serious medical evaluation to determine the cause of his lingering illness.

"I am worried about it," White said. "He's in rough shape. He's in really bad shape and we're going to have to do some stuff to take care of this guy. He is not well and he's not getting any better."