Belfort's career resurrection came with the help of testosterone replacement therapy, which is now illegal in Nevada.
Most of the UFC's events are held in Las Vegas, and it's also likely that other state athletic commissions will follow suit and ban it in other states, so Belfort is going to have to figure out how to manage his career without it.
For now, Belfort's fight at UFC 173 in May is off. Lyoto Machida will replace him and fight middleweight champion Chris Weidman for the belt.
Apparently Belfort and his camp decided that they needed some extra time to clean out his system and prepare for the fight without TRT assistance.
He released a statement about his decision:
We'll see if Belfort can come back strong but for now, Machida will get a crack at the belt.