The game's street date isn't until Tuesday, but someone already has the Xbox 360 version and uploaded this video, found by Pasta Padre, in which the Xbox Live menu is greyed out and displays an advisory that a code is needed to access online features. The code's free in every new retail copy of the game, or may be purchased through the Xbox Live Marketplace, or PlayStation Network for PS3 version owners.
THQ remained mum on the subject throughout the week but just released a statement confirming the code and its $US5 price. "This multiplayer content for UFC Undisputed 2010 will be available via a one-time code included with the game at purchase. Codes for accessing the content will be available for second-time buyers for an additional $US5."
From the video linked, it looks like the code covers all of the game's multiplayer content, not just the "Fight Camp" mode touted in THQ's statement. But it's unknown if any free trial period will be available for those who rent the game. THQ's statement said more details will be forthcoming at the game's official community site.
Confirmed: UFC 2010 Requires Code for Online Play [Pasta Padre]