Heavy.com has the scoop:
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. 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.
A UFC source confirmed the story while pointing out that Lesnar was never officially part of the UFC 108 card.