By far the best and most popular mixed martial arts fighter who isn't already under contract to Ultimate Fighting Championship is Fedor Emelianenko, a Russian heavyweight. And UFC's inability to get Emelianenko under contract has been one of the organization's few failures.
In an interview with Sherdog, Emelianenko's manager said UFC's financial offer is solid, but that its contract is quite restrictive?
Sherdog.com: As Fedor's manager, can you please fill us in on the current state of his contract negotiations.
VF: At the moment we are in negotiations with a number of organizations who have put offers on the table. I'll be blunt in saying that the UFC offer is the most financially attractive one. However they are very harsh in their terms and are not very flexible in actually negotiating them.
Fedor has now been the PRIDE heavyweight champion for four years and I think we have earned the right to negotiate a contract that suits both parties. Instead we are faced with a blunt "you are either in or you're out." This does not really suit us. If the negotiations continue in a similar manner, we'll prefer to fight for less money but with an organization which is more flexible.
The problem is that Fedor is the face of Combat Sambo in Russia. His popularity is at a level where he is acquainted with president Putin himself, in part because he is so successful and well known for Combat Sambo here.
As UFCJunkie notes, UFC would have a lot to lose if the deal doesn't go through. Dana White needs to get it done.