If the Irishman lands the craziest of flukes it will propel him to a greater height than even he might have dreamed – and would be a disaster for boxing

What if the impossible is possible? What if a foot slips, a hand drops, a lucky swing lands right and Conor McGregor knocks Floyd Mayweather cold in the craziest of flukes?

What if everybody with any good sense is wrong, and Mayweather at 40, having not fought in nearly two years, is no match for McGregor? What if the loudest mouth in UFC turns out to be the better boxer on Saturday night? What if Mayweather’s 49-0 becomes 49-1 and the result isn’t even in doubt? Well, what then?

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Few experts feel McGregor, the UFC’s lightweight and former featherweight champion, has a chance in a boxing match against this generation’s most dominant boxer. But scarce were the experts who believed Donald Trump could beat Hillary Clinton, or that Buster Douglas would defeat Mike Tyson. The unimaginable sometimes does happen. And if it does, if McGregor really beats Mayweather, it will propel him to a greater height than even he might have dreamed.

“If you look at this thing and you look at how big this fight is and you look at how big these athletes are that are involved in this fight … if Conor does knock Floyd Mayweather out, he’s the biggest athlete on earth,” UFC president Dana White said in June. “He’s the biggest athlete [on this planet] – on other planets – he’s the biggest athlete. It’s pretty crazy.”

But what does being the biggest athlete as an MMA fighter mean? McGregor, who dazzled White as a brash, unproven fighter in 2013, has climbed so fast in UFC it’s almost as if he runs the organization himself – dictating who he fights and what belts he tries to claim. After his 13-second knockout of Jose Aldo in UFC 194, his exhausting side-battles with Nate Diaz and his destruction of Eddie Alvarez that made him the first UFC fighter to hold two titles at once, there isn’t much left for him to accomplish in MMA. Even before talk of the Mayweather fight he seemed to be running out of achievements to chase.

It was only five years ago that McGregor was collecting welfare checks while trying to build an improbable mixed martial arts fighting career in Dublin. In that short a time he has made himself one of the world’s most recognizable athletes – a single-name sensation in a sport that, aside from Ronda Rousey, has not had many breakout mainstream celebrities. But that also has some limits.

Going back to UFC and resuming his foul-mouthed, insult-laden press conference sideshows will not make him transcendent, or bring the outrageous paydays he demands. While he may continue in UFC he, like Rousey, might have a bigger future away from MMA.

“He’s one of those guys you can see on Dancing With The Stars or crossing over to television shows,” Bob Dorfman, the executive vice-president of Baker Street Advertising, told the Guardian. “He’s got name and face recognition and he’s also got a real out-there personality.”

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But as much as McGregor’s name will get bigger, it’s hard to imagine Mayweather’s shrinking. His 49 victories have come against some of the best boxers of his era. Twenty-six of those past 31 bouts have had a title on the line. He has dominated for more than two decades and losing to a mixed martial artist aged 40 will not wipe that record away. His legacy has been winning all the boxing matches that mattered. Aside from not allowing him to surpass Rocky Marciano’s 49-0 record, a loss to McGregor will be an outlier – one of those dumb decisions people make for money – but it won’t tarnish the legacy of an undefeated boxing career.

A bigger issue is what a defeat might do to boxing. For years, the sport has suffered from an image problem, combating perceptions of corruption while a sea of organizations claim so many champions it’s hard to keep track of who truly is the best boxer at each weight. While UFC has probably not surpassed boxing, it has become a well-packaged, overly controlled alternative offering single champions for each size and compelling match-ups.

In a telling example of how the two sports have shifted, one of MMA’s harshest critics, US senator John McCain, who famously called it “human cockfighting”, instead praised UFC to the Guardian last year, saying “the MMA has cleaned up their act,” while denouncing boxing as “an alphabet soup” of champions.

A McGregor victory over Mayweather may only bring more eye-rolling about boxing and siphon potential fans either to MMA organizations like UFC or simply drive more people away from boxing for good. It might set in the minds of a new generation of sports fans that boxing is just a punching sport and perhaps not as complete a fight as MMA. If McGregor wins, will there be another pay-per-view boxing star like Mayweather?

“It would definitely be great for MMA if McGregor won,” Dorfman said. “Aside from the monumental events there is no enticement to follow boxing these days. Who are the champions at each level? There’s not a lot of exposure to the fights aside from a pay-per-view level.”

Could the image of Mayweather lying flat on the canvas or slumping away in defeat become another blow for a sport that could use a big hit? Especially with current face of the MMA walking away with his fists upraised and his hands in boxing gloves.