Dana White is confident Conor McGregor will be "the biggest star on earth" on Saturday by becoming the first man to beat Floyd Mayweather Jr.
UFC superstar McGregor will make his boxing debut in Las Vegas after luring Mayweather out of retirement for the blockbuster event.
Given Mayweather's 49-0 record the American has been installed as strong favourite for the fight, but McGregor's odds have continued to come in as the bout draws closer.
And UFC boss White believes McGregor is going to shock the world by knocking out his illustrious opponent, and in turn make him the "greatest combat sports star ever".
"To think Conor can't beat Floyd Mayweather is quite something," White told BBC Sport.
"The naysayers will be asking different questions on Sunday. This is not a boxing match, it's a fight.
"He is completely different to anyone I have ever met. His belief in himself, his fight IQ, if he hits Floyd Mayweather he will hurt him and knock him out.
"Every time I've seen him he is in great shape.
"His legacy will be that he is the greatest combat sports star ever. If he knocks him out he will be the biggest star on earth."