BJ Penn declares that he and Nick Diaz are in a "must-win situation" when the two face each other in the main event at UFC 137 according to mmaweekly.com.

"I kind of look at it, we're both in a must-win position. I love to do this. I love to do mixed martial arts. I love fighting for the UFC...Nick's here to prove himself, that he's here to stay, and that he is a title contender," Penn said.

Both men have already distinguished themselves in the sport; Diaz is Strikeforce's former welterweight champion while Penn is the UFC's former lightweight and welterweight champion. The winner of their bout will no doubt be at the top of the UFC welterweight's contender list.

Diaz (25-7 (1 no contest)) is riding a 10 fight win streak as he faces the 16-7-2 Penn. Penn's last bout was a draw against Jon Fitch at UFC 127.

"Both of us have a lot of pressure on us come Saturday night," Penn added.

UFC 137 is scheduled for October 29 with Penn vs. Diaz to headline.