The all-time pay-per-view record was set in 2015, when 4.6 million customers purchased a boxing match between Floyd Mayweather and Manny Pacquiao. If the upcoming Floyd Mayweather-Conor McGregor fight is going to break that, it will have to do it without at least one customer.

Manny Pacquiao himself.

“The real fight and the best fight is [Gennady] Golovkin vs. Canelo [Alvarez],” Pacquiao told Yahoo Sports. “The best vs. the best. That’s the fight I will be watching.”

Golovkin-Alvarez takes place on September 16 and has any true boxing fan excited. Mayweather-McGregor, which goes off in Las Vegas on August 26, is all but acknowledged to be a sideshow of an event.

McGregor, 28, is a mixed martial arts star from the Ultimate Fighting Championship who has never fought as a professional boxer. Mayweather, 40, is considered the best boxer of this generation and, at 49-0, one of the best all time. He’s particularly adept at slipping punches and making otherwise great fighters look clumsy.

Like many in boxing, Pacquiao sees this is as some kind joke.

“McGregor has no chance in this fight,” Pacquiao said. “In fact, it could be very boring.”

Floyd Mayweather (L) won a unanimous decision against Manny Pacquiao when the two fought in 2015. (Getty) More

Pacquiao fights Sunday in Brisbane, Australia, against undefeated Jeff Horn (9 p.m. ET, ESPN). It’s a big fight Down Under, with the possibility of more fans attending than even the 51,000 who watched Pacquiao defeat Joshua Clottey in AT&T Stadium in 2010. At 59-6-2, Pacquiao is on a two-fight win streak since losing to Mayweather but is winding down his career. He also serves as a senator in the Philippines and may one day run for president.

Had Pacquiao defeated Mayweather back in 2015, rather than lose a dull decision that angered many pay-per-view buyers, it might be the Filipino cashing a monster check to fight McGregor.

That isn’t how it worked out, though. While McGregor still would have been a prohibitive long shot, it would have been more promising than facing Mayweather. Pacquiao is prone to brawling on occasion, perhaps opening himself up to something. Mayweather is unlikely to take that bait.

Mayweather, per Pacquiao, is simply too great a defensive fighter and counter puncher for a novice to deal with.

Pacquiao built his reputation on speed, accuracy and the ability to repeatedly bludgeon opponents in becoming one of the very best of his era.

In 2010, he destroyed Antonio Margarito in part by landing an absurd 58 percent of his power punches, 411 of them in total. Margarito didn’t leave the hospital for a week.

Yet against Mayweather, he got almost nothing done. Pacquiao landed just 81 punches (jabs and power) total, according to CompuBox.

So count him skeptical that McGregor can even manage that. And forget the idea that he’ll land some haymaker and change everything.

“There is no way he will be able to land a meaningful punch on Floyd,” Pacquiao said. “How could he? He has no professional experience in boxing.”

This is the perception that promoters, not to mention the fighters themselves, will have to battle through to sell the fight. Both Mayweather and McGregor are masters at generating publicity and their pre-fight press conferences and interviews will likely be wild, boorish and impossible to ignore.

Still, the idea of a mixed martial artist, even one as good as McGregor, switching sports is a tough argument to make. Already Mayweather’s camp has been talking up McGregor and suggesting he has a puncher’s chance against an aging Floyd … which may be the surest sign of the challenge.

At the end of the day, will people pay out nearly $100 for this?

Pacquiao, as well as anyone, knows how hard it is to fight Mayweather. It was just over two years ago that he trained and then tried to do it. The challenge was like no other bout in his career. Cracking the code on a guy with incredible speed, defensive instincts and ability to hit and move proved impossible.

Story continues