Undefeated Mayweather will take on Irish UFC star McGregor in Las Vegas next Saturday in a fight that is expected to break pay-per-view records.
Many have doubted the credibility of the high-profile affair, however, with British boxing great Lewis the latest to question exactly why it has been given the green light to go ahead.
"There is tremendous build-up and hype but I don't really take it as a serious fight," he told BBC Sport. "I wouldn't count a fight like this as a 'fight'. He's basically boxing a guy that is a UFC fighter and not a boxer.
"Everybody wants to know what's going to happen. Is McGregor going to throw a kick because, obviously when he resorts to boxing and realises he is no match for Mayweather, what will he do? How will he get around that?
"No other boxers from 49 fights have figured out how to beat Mayweather - now a UFC fighter that doesn't even have a boxing career is trying to beat him at boxing - I think it's a farce to a certain degree. I don't think it is a fight that I am going to jump on a plane and go to see unless they pay me to commentate on it."