It appears that Forrest Griffin wasn't a fan of fighting Vitor Belfort at UFC 155 in December. Belfort spoke to Brazilian site UOL about the issue, and said that Griffin wasn't interested in tangling with him at the Vegas event:
I met with Forrest and he told me that he volunteered for a list of six names and mine was the first. He said he would face any of them except me. It's good to have this kind of recognition. I am here to serve the company."
I think this probably has to do with the fact that the two men were training partners for so long at Xtreme Couture. I can't see any other reason why Griffin would turn down a bout with The Phenom, only to sign on against Phil Davis. Belfort also stated that he's willing to take fights at either light heavyweight or middleweight:
"My weight, my category, are the medium. I am adaptable. But I do not have much time left in my career and I want to have great challenges, be in whichever weight it will be. I can make great fights and don’t run from anybody, I’ll be always ready."LINK