Well, "The Greatest" took exception to that.
Ali took to his Twitter account Monday to send out the following message to the masses, especially Mayweather.
"Don't you forget, I am the greatest! #MuhammadAli," Ali tweeted in a clear response to Mayweather's bold declaration.
The tweet was accompanied by the famous shot of Ali celebrating his win over Sonny Liston.
Ali's reminder came just five days away from Mayweather fighting Manny Pacquiao in their mega bout on May 2 live from the MGM Grand Garden Arena. Late last month, Ali's daughter said her dad would be rooting for Pacquiao against Mayweather.
At the time, Ali's daughter Rasheda Ali told TMZ Sports: "My dad is Team Pacquiao all the way! My dad really likes Manny. He's a huge fan of his. He knows Manny's a great fighter, but it's more about what he does outside the ring. He's such a charitable person."
Although Ali didn't enjoy an undefeated record at 56-5, he touched the hearts of millions of fans with his memorable bouts and admirable stands outside the ring. Mayweather will be seeking his 48th career victory.
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(Photos from left: Michael Buckner/Getty Images for Fight Night, Stephen Dunn/Getty Images)