The UFC welterweight championship will be contested for just once in 2007.

Matt Serra (Pictures), who claimed the belt with a shocking win over Georges St. Pierre (Pictures) this April, suffered herniated discs in his lower back Monday, forcing him to withdraw from his anticipated Dec. 29 title defense against former two-time 170-pound champion Matt Hughes (Pictures), the UFC announced Thursday.

Serra and Hughes, who share a healthy rivalry, are coaches on "The Ultimate Fighter 6" and would have fought in the co-main event of UFC 79 at the Mandalay Bay Events Center.

According to UFC.com, Serra, a Brazilian jiu-jitsu black belt under Renzo Gracie (Pictures), was injured while demonstrating a move following one of his training sessions. A subsequent MRI revealed the severity of the injury.

"This is the hardest thing I've ever had to do," Serra said in a statement on UFC.com. "I've never had a back injury before; I could hardly get off of the MRI table. There is no way I can train through this, and I'm devastated, especially because this was such an important fight. I was looking forward to fighting Matt Hughes (Pictures). All my training was going phenomenally until Monday. All I can do now is to get better and to fight again as soon as possible."

The UFC neither named an replacement for Serra, nor announce whether Hughes would remain on the card.