I just got this a minute ago from UFC:
The Ultimate Fighting Championship® (UFC®) organization today announced UFC Welterweight Champion Georges St. Pierre has been forced to withdraw from the Feb. 3rd UFC 67: ALL OR NOTHING card due to a knee injury suffered during training for his first title defense against Matt Serra. The rest of the card, which includes the UFC Middleweight title bout between Anderson "The Spider" Silva and Travis Lutter, as well as the UFC debuts of Quinton "Rampage" Jackson vs. Marvin Eastman and Mirko "Cro Cop vs. Eddie Sanchez remain intact.
"Unfortunately, Georges St. Pierre was injured in training and we're hopeful that he'll recover quickly," said UFC President Dana White . "We look forward to having Matt Serra's title fight as soon as we can."