Yoel Romero weighed in at 185.2 pounds at his second attempt to make championship weight.
The 41-year-old's opponent, middleweight champion Robert Whittaker, hit 185 pounds earlier during the weigh-ins. Romero earned a third-round KO victory as a plus-150 underdog, but was deemed ineligible to claim the belt after failing to make weight.
There is no word from the UFC if the fight will proceed and how the purses will be divided. However, Romero is no longer eligible to win the title.
Initially, Romero came in at 186 pounds.
"The main event is on".
The Cuban fighter was approached by Whittaker yesterday, with the Kiwi born fighter telling his rival not to worry and that their MMA bout will still go ahead at UFC 225. "Why would I? I might as well fight someone heavier than me".
If he loses focus, he know he could find himself in line for yet another rematch.
"But I tell you what, I've got a bag of new tricks that I'm looking forward to bringing out and throwing at him".
Holly Holm (-210) is favored against UFC debutante Megan Anderson (+180) in what amounts to a women's featherweight title eliminator.
Breakout Sydney heavyweight Tai Tuivasa (7-0) faces his toughest test yet in Andrei Arlovski (27-15), a veteran of 25 UFC fights.