Four-weight world champion Mikey Garcia will move up two weight divisions to take on IBF world welterweight champion Errol Spence Jr on 16 March.
Garcia, 30, still holds the WBC title in the 135lbs lightweight division and will move to 147lbs to face Spence Jr.
Spence Jr, 28, won his title from Britain's Kell Brook in May 2017.
"Floyd Mayweather did it all the time, fighting bigger guys," said Garcia. "He did it with skills. There's more to boxing that brute power."
Garcia has held world titles at featherweight, super featherweight, lightweight and super lightweight, amassing a record of 39 wins from 39 bouts.
A unification bout with WBA lightweight champion Vasyl Lomachenko had been rumoured before a March meeting was confirmed with fellow American Spence Jr in Arlington, Texas.
Garcia now claims he is pleased some are choosing to write him off because of the weight jump, with a number of people on social media pointing to a notable size difference when the two fighters posed head to head.
"That's why I took this fight," he added. "That's what I want. Once I do this I will prove to everybody that I am a better fighter than people expect. These kind of victories will open the eyes of doubters."
Spence Jr has a record of 24 wins from 24 bouts, 21 via stoppage.
Should Garcia win, he would join the likes of Mayweather, Tommy Hearns, Manny Pacquiao, Sugar Ray Leonard and Oscar de la Hoya in winning world titles across five weight classes.