A knee injury has forced Shane Carwin out of his Dec. 15 UFC bout with Roy (Big Country) Nelson.

The two heavyweights have been serving as rival coaches on Season 16 of "The Ultimate Fighter" and were due to fight Dec. 15 in the main event of a televised card in Las Vegas.

"WOW!! It never ends Carwin blew his knee out. Looking for a new opponent for Roy on the TUF Finale on FX," tweeted UFC president Dana White.

In other injury news, Jim Miller is stepping in for an injured Gray (The Bully) Maynard against lightweight Joe Lauzon at UFC 155 on Dec. 29 in Las Vegas.