Diaz was originally slated to face GSP on this card but, due to his failure to show up for media events, he was bumped down to face Penn and Condit took his spot.
Diaz is the former Strikeforce welterweight champion and Penn is the former UFC lightweight and welterweight champion.
Both fighters possess the ability to knock out or submit the other. Something has got to give in this main event.
On top of the main event, the co-main event features Cheick Kongo coming off his impressive come-from-behind win over Pat Barry in June. Kongo will face TUF alum Matt Mitrione in a heavyweight showdown where somebody is getting knocked out.
On top of the main event and co-main event is the possible last fight of MMA legend Mirko Cro Cop, who has now suffered back-to-back losses. Cro Cop faces the hard-headed Roy Nelson in yet another heavyweight showdown.
Stick here for Bleacher Report's coverage of the weigh-ins with Antwyn Jackson and Sal DeRose.