Well the five likeliest options are
Fabricio Werdum close to Cormier in the rankings and a win puts him next in line for a title shot.
Cheick Kongo 4-1-1 in his last five, Kongo is a UFC gatekeeper and likely working as a training partner for the UK show.
Mirko Cro-Cop CC is always game, if he's healthy he'll main event.
Andre Arlovski Arlovksi is basically on a three fight win streak the UFC is all about giving guys second chances.
Gabriel Gonzaga fighting on the brazil prelims he's trained and he's big enough of a name that he could come in as a replacement.