Sources close to Brock Lesnar's camp informed Heavy.com tonight that Lesnar will not be able to participate in the postponed main event of UFC 108 against Shane Carwin.*

Lesnar has battled an undisclosed illness for the past month that forced him to withdraw from a scheduled title defense against Carwin at UFC 106.

Heavy.com has been informed that the disease is actually mononucleosis, commonly referred to as "the kissing disease."

The bout was rescheduled for UFC 108, but Heavy.com learned earlier this week that Lesnar has not recovered from the illness and cannot train at even a moderate page without quickly becoming exhausted.

Sources close to the UFC confirmed the story while pointing out that Lesnar was never officially part of the UFC 108 card.

This is yet another major blow to the UFC 108 card, which lost a potential Anderson Silva/Vitor Belfort middleweight title fight last week when Silva withdrew because of elbow surgery.

The current main event for the show is Rashad Evans vs. Thiago Silva, but it likely will not be the main event come Jan. 2.

Rumors have swirled today regarding a potential Cain Velasquez vs. Antonio Rodrigo Nogueira bout for the card, but sources in Cain's camp denied the story.