When Mayweather retired for the second time after beating Andre Berto in an unspectacular but dominant win over the fellow American, it looked as though he would never achieve that 50-0 landmark.
Of course, the difference between going 49 fights and 50 fights unbeaten is minimal – both are remarkable records and few will fail to count Mayweather among the best boxers of all time because of it.
However, “Pretty Boy” is tarnishing his record with a gimmicky bout against UFC star McGregor and living up to his latter nickname – “Money” – rather than his former one.
It may be that is exactly as Mayweather wishes.
It was when he split with promoter Bob Arum and started running his own show that he preferred to be known for his financial acumen than his super-sharp boxing skills. He may wish to reinforce that image.
But there is little doubt that he will win and win well against McGregor, a talented boxer with a decent left hand but only dangerous in a context where his fists are just part of an armoury as opposed to his sole weapon.
There is little doubt too that Mayweather will make a record-breaking amount of money out of the fight, perhaps as much as £300million.
But it cannot simply be about money and a tax bill reported to be as many as nine figures long.
Irrespective of his financial ups and downs, Mayweather wants people to remember his talents with his hands and feet. And by fighting McGregor, he has tainted whatever legacy he had, and in doing so has changed the course of American boxing forever.
Mayweather was rarely a spectacular fighter in his later bouts. Of his last 10, only one win has come by knockout. A skilled defensive boxer, he does not go to war and slug his opponents in the fashion that your average punter wants to see.
Even his record-breaking win over Manny Pacquiao, watched by more paying customers than ever before was a disastrously poor flop. Of the 4.6m people who bought the fight, a good number would have rather had their money back.
But boxing aficionados relish his presence in the ring and his finely polished avoidance techniques and Mayweather is caught between trying to please the public, the fans and the tax man.
The billion-dollar man has not been shy about the main reason behind fighting McGregor – it’s called “The Money Fight” for goodness sake. He has not been goaded into it by the trash-talking of the Irishman or the suspicion that he is too old to beat him.
It is a business decision – but with an undertone of ego. I think Floyd believes he can save American boxing.
At present, it is in a sorry state. Gone are the days of a heavyweight division dominated by homegrown talent, regularly facing off at MGM Grand or Madison Square Garden.
Then, as Mayweather’s star was on the rise, so his country’s interest in boxing was on the wane.
By the time he won his second world title in 2002, the ship had already sailed. American football, basketball, baseball and in parts even soccer now have far surpassed it as their personalities and heavyweight contests began to outweigh those inside the ropes.
Mayweather thought he could fix it, by coming back again, to save the world by booking a fight no-one thought was even legal when it was first mooted.
This fight, boxing powers over the Atlantic hope, will reignite the passion for the sport and start the fightback against the other mainstream attention-seekers.
But it is just a sham and one the public will quickly forget when it is inevitably over in a one-sided demonstration of the fact that good boxers win boxing matches against non-boxers.
All they are doing is taking one of the few fighters who will be remembered as a great and ensuring that the younger generation remember him as he is known – “Money”.
McGregor Mayweather may be a terrific spectacle. It may be exceptionally entertaining. But it is not a boxing match, and Mayweather should finish it 49-0 (1-0). This is not his 50th.