Martin Kampmann (Pictures) has been forced to withdraw from his June 16 fight against former UFC middleweight champion Rich Franklin (Pictures) after sustaining a serious injury to his left knee that could require surgery.

The Danish striker was set to make his UFC main event debut in Belfast, Northern Ireland, but his exit from the fight has sent Zuffa scurrying for a replacement.

"It was a big opportunity for me to prove I belong in the big leagues," Kampmann told Sherdog.com. "So I'm very disappointed."

Undefeated in three UFC fights, Kampmann, an undersized middleweight known for his technical striking and underrated work on the floor, now must wait for swelling to go down before he receives final word on the severity of the hyperextension he suffered Friday while grappling at Xtreme Couture in Las Vegas.

"I'm really worried about getting my knee back to 100 percent," said Kampmann (15-2-0). "That's my primary concern right now."

Speculation on a new opponent for Franklin has centered on middleweight contender Yushin Okami (Pictures) (20-3-0), though UFC sources have denied a deal is in place to set up a Franklin-Okami showdown.

With a win in June, Franklin (21-2-0) could be positioned to make another run at the UFC middleweight crown he held from June 2005 through October 2006.