Crawford, 37, from Omaha, Nebraska, has won world titles in four weight classes and is undefeated in 41 fights. He's been undisputed champion at both super-lightweight and welterweight. His most recent wins came against Israil Madrimov and Errol Spence Jr.
In a chat with Club Shay Shay, Crawford didn't hold back his praise for Mayweather.
"Floyd beats everybody … I don't know but it'd be tough, Floyd, man, that boy's the GOAT, that boy's bad."
Mayweather retired in 2017 with a perfect 50-0 record. He won world titles in four weight classes and beat some of the biggest names in boxing. His win over Manny Pacquiao stands out, along with victories against Oscar De La Hoya and Canelo Alvarez.
Crawford aims to finish his career without losing, just like Mayweather did. He's got a big fight coming up later this year against Canelo Alvarez, which will test that goal.
Mayweather's last fight was a win over MMA star Conor McGregor in August 2017. It was a unique cross-over bout that capped off an incredible career.
Crawford's words carry weight. He's achieved so much himself, but still puts Mayweather on a pedestal above everyone else. It's a testament to just how good Mayweather was in the ring.