For all the talk that has built up around the putative showdown between Floyd Mayweather and Conor McGregor being about the best pound‑for‑pound boxer of the past quarter of a century taking on the brightest star in the history of mixed martial arts, it is not. It has all the hallmarks of a mismatch. This one, like nearly all the others, is about the money.

Unless there is an accident or a miracle, Mayweather will bamboozle the Irish cage fighter to the point of embarrassment with skills that carried him unbeaten through 49 professional boxing matches and garnered him titles at five weights in 26 world championship contests. Although McGregor, 28, is a phenomenon in his own discipline, he has not fought competitively with proper boxing gloves since he was a 15‑year‑old novice in south Dublin. As his trainer at the Crumlin amateur club, Phil Sutcliffe, told Boxing News last year: “He won a few novice titles and boxed on plenty of shows [over three years] to learn his trade but, before he became a junior, he found another love [kick‑boxing and mixed martial arts] and packed it in.”

Sutcliffe, a respected figure in Irish amateur boxing, sees remnants of those long-ago boxing skills in the UFC performances of the switch-hitting McGregor, particularly his southpaw left-cross finisher, a lethal blow that has accounted for many of his 24 MMA opponents over eight years. But even Sutcliffe surely does not expect McGregor to beat Mayweather.

Whatever advocates of MMA will shout in a bar or on the internet, this is not a fair fight. McGregor, who has won 21 bouts and lost three (all by submission), will do well to land the occasional blow on the twisting shoulders of the boxer regarded as the best defensive ring artist of the past 25 years. If it lasts more than a few rounds, it will be because Mayweather has been out of the ring for nearly 18 months and turns 40 on Friday.

While they are roughly the same size, Mayweather is stronger, quicker, slicker and more seasoned, having boxed consistently at the welterweight limit of 147lb throughout the last decade of his career, as well as moving up to win the world 154lb light‑middleweight title. In four years with the UFC McGregor has operated in a similar weight range, between 145lb and 155lb, although the divisions in his sport allow for a wider disparity.

Floyd Mayweather is the shrewdest businessman in boxing since Sugar Ray Leonard. Photograph: Earl Gibson III/Getty Images

It will make little difference: the real gulf between them is in boxing ability. While McGregor insists he is chasing down some sort of unique fistic history, he also admits he is in avid pursuit of the cash.

The Irishman does not lack for charisma. He is brash and, generally, he delivers on his predictions – never more spectacularly than on the December night in 2015 when he knocked out José Aldo in 13 seconds with a perfect left hook. “Precision beats power,” he said in the octagon afterwards, “and timing beats speed.” He understands the core fundamentals of fighting, as Sutcliffe has said.

Nevertheless, for all that he might regard himself as the co-star in a production yet to be signed off, McGregor knows why this bout makes sense. As does Mayweather, the shrewdest businessman boxing has had since Sugar Ray Leonard.

Take a deep breath and absorb some numbers: Mayweather generated a staggering $1.3bn in pay-per-view revenue in 15 fights over the last 10 years of his career. In three years between 2012 and 2015 he earned more money than any other athlete in the world, according to Forbes and Sports Illustrated. When he fought Manny Pacquiao in May 2015, there were 4.6 million fans willing to pay for the privilege, bringing in $400m in 36 minutes of boxing on a single night.

For every millionaire in boxing there are a thousand mugs who helped them get there. Mayweather is one of the few to have beaten the odds. McGregor has not done badly either and his sport is on what seems to be an ever-upward curve, especially among young punters disillusioned by the serial shenanigans of professional boxing. McGregor is not doing this for UFC, though; he is doing it for McGregor.

As Damon Runyon, that old rascal of the fight game, once said: “Always try to rub against money for, if you rub against money long enough, some of it may rub off on you.”

So, do not worry that McGregor is out to strike a blow for boxing’s young tearaway half-brother, as exploited and sold with increasing success by Dana White’s UFC company. McGregor, White’s biggest attraction by a distance, is a wilful and outspoken individual who pays his boss few compliments and creates as much controversy as he does bruised heads and knuckles. But he is sucking on the teats of the greatest cash cow in the history of sport and they both realise they are running out of time.

Mayweather’s farewell appearance, outpointing Andre Berto over 12 dull rounds in September 2015, excited a mere 550,000 viewers on PPV, his poorest return since 2006. He figured it was time to get out, with his collection of 90-odd high-end sports cars and limousines, a man-cave of a mansion situated on an exclusive Las Vegas golf course, private jets and an untamed ego.

Nothing, it seemed, would tempt him back to the ring – not even the chance to break Rocky Marciano’s record of 49-0, giving his critics even less reason to question his greatness. Until McGregor came along. He spotted his tormentor as an easy mark, much as old fighters did when challenged by young toughs in the travelling boxing booths.

One-sided as this fight would be, there is hidden danger for Mayweather. Although McGregor’s pure boxing skills are long buried, he is practised in the art of crude hurting. He could land that long left, or his trademark uppercut. Mayweather might just get old on the wrong night. There has to be some element of doubt, otherwise even the most naive customer would not be interested.

But, as Runyon also said: “I long ago came to the conclusion that life is six to five against.” And you will get far longer odds than that on McGregor if this fight ever happens.