People telling me Mayweather will have his hands full trying to land on McGregor -STOP IT! I respect McGregor BUT i ain't Floyd and i landed
His straight left hand from the southpaw stance has become one of the fight game's most dangerous weapons, making McGregor the first simultaneous holder of two UFC belts in history.
But if he's such a good boxer, why did he depart the sport as a teenager? Has McGregor profited from a string of grapplers who lack skills with their hands?
Paschal Collins, Ireland's seasoned boxing trainer, remembers an unknown MMA enthusiast who was at home in the boxing gym. "Four years ago, I always reckoned that he could have gone all the way in boxing for the reason that his work ethic is unbelievable," Collins told Sky Sports. "He trains - no, he practises - three times a day.
"You know when somebody walks into a room and they stand out? He had a confidence but behind the scenes he keeps his head down. I would watch him for an hour and he'd practise the same move over and over. He stood out, absolutely.
He sparred my nephew Stevie Jr, a cruiserweight, and showed no fear even when he was clipped.
"He's brave, he's got a heart, and he's afraid of nobody. He sparred my nephew Stevie Jr, a cruiserweight, and showed no fear even when he was clipped."
Before McGregor's growth took him through Collins' pro gym, he first learned to wrap his hands in the Crumlin Boxing Gym, an amateur establishment rife with young Irishmen learning about the discipline of the ring.
"He was like any other novice who we taught the basics to," Crumlin coach Phil Sutcliffe told Sky Sports. "He could have been very good if he stayed with boxing.
"Some kids had more talent than Conor but didn't work as hard and eventually he found them out. He has skills from his time here - his hands up, his chin down, his elbows in. When he got good enough he was able to drop his hands because he could read the punches. He's a very, very good reader.
"He's ambidextrous, we teach that to all our kids, he can box orthodox or southpaw. His straight left changes fights. It's an opportunist's punch - he's always had the ability to turn on his back leg to throw his back hand."
McGregor took his boxing skills to the cage and exploded onto the UFC scene four years ago, immediately demonstrating an understanding of range that dumbfounded rivals.
The same weapon that impressed his first coach Sutcliffe was still getting the job done. Three uppercuts accounted for Marcus Brimage in McGregor's 2013 debut, then the same left hand made him the first-ever simultaneous two-weight champion against Eddie Alvarez last November.
"A southpaw's best weapon is the straight left," McGregor's current coach John Kavanagh told Sky Sports. "For whatever reason, nobody hits harder than Conor.
"Contrary to popular belief, it tends to be tall, lanky, rangy fighters who punch the hardest. Conor has a genetic X-factor when it comes to punching - even I don't know exactly what that is. It's hard to find a better system than western boxing to teach you how to hit as hard as possible."
Super-middleweight world champion George Groves has been an impressed onlooker but when quizzed whether McGregor could cut it inside the boxing ring, he noted a crucial different in the Irishman's style.
They attack from so far out. Do that in boxing and a skilful boxer would time you.
"They have to worry about takedowns so they have to throw punches from a much wider distance," Groves explained to Sky Sports. "They can get away with things that we can't in boxing - for example they attack from so far out. Do that in boxing and a skilful boxer would time you.
"We're used to fighting much closer but if the UFC guys do that, they're likely to be grabbed. They certainly have power, but in UFC they don't throw combinations. If you're a pure boxer you won't last long inside the cage - but vice versa."
Yet McGregor's sole UFC defeat, a submission loss to Nate Diaz last year after tasting some of his own medicine when stood toe-to-toe, led to criticism from Tyson Fury. "Boxing is the ultimate combat sport," Fury tweeted. "Where two proper fighters stand up and fight."
McGregor's low-profile appearances in California-based boxing gyms in the build-up to his rematch with Diaz is when the wheels really began turning with Floyd Mayweather - although, it led to sparring with Chris van Heerden which didn't impress purists.
His defeat to Diaz was attributed to a lack of boxing finesse by his own striking coach Owen Roddy, and it needed to be corrected.
"He was winning the fight but punched himself out," Roddy told Sky Sports. "He was trying to force the finish. He was landing his shots but, because Diaz was able to take them, Conor was throwing higher and higher combinations and got exhausted. The tables turned.
If we stick to popping shots and moving, I think he'll put Diaz away.
McGregor's coach Owen Roddy
"Conor was trying to knock him out with every punch and was putting too much behind every shot. If we get him to only put power behind certain shots, he should reserve his energy more."
McGregor is the latest in a fabled line of punchers from Ireland and counts former world champions Wayne McCullough and Steve Collins as fans, while Lennox Lewis has tweeted support. Now McGregor must throw his first punch as a boxer on the biggest possible stage.