By Joseph Santoliquito

PHILADELPHIA, PA (CBS) — As Floyd Mayweather and Conor McGregor embark on their four-city press tour this week, covering Los Angeles, Toronto, Brooklyn and London, England, there will be many fans and media alike sitting out there wondering if “The Notorious” has any chance to giving Mayweather his first pro defeat.

The reality is an unequivocal “No!”

But there is a very minute chance that McGregor, a 29-year-old southpaw, could pull off what would be the largest upset in sports history, ranking up there with Francis Ouimet beating golf giants Harry Vardon and Ted Ray at the 1913 U.S. Open. The difference is that Ouimet at least played golf and was an accomplished amateur.

A McGregor upset would transcend that because he never boxed—not even as an amateur. Granted, McGregor is a UFC and mixed martial arts superstar, stepping into the boxing ring with one of the best all-time fighters in boxing history will be like stepping on Mars for The Notorious.

The last time Mayweather (49-0, 26 KOs) lost was on August 2, 1996, in a 10-9 decision to Bulgaria’s Serafim Todorov in the featherweight semifinal round of the 1996 Atlanta Olympics. As a pro, he’s had few eyebrow-raising moments, like on April 20, 2002, in his first fight against Jose Luis Castillo, who imposed his superior size that forced Mayweather to cede comfort distance; and on May 1, 2010, against Shane Mosley, whose straight right hand with 2:06 left of the second round is probably the hardest punch ever landed against “Money.” Another Mosley right with 1:15 left in the round buckled Mayweather’s knees. Then Mayweather proceeded to dominate every second of every round thereafter.

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There are a few things that have to be factored into McGregor’s chances: One, Mayweather turned 40 on February 24; and two, when Mayweather steps into the ring against McGregor, it will be almost two years since his last fight. McGregor, though it was an MMA fight, stopped tough Philly fighter Eddie Alvarez in November 2016.

McGregor’s best opportunity against Mayweather is to jump him early. He’ll need to land a big left and do it within the first three rounds, because after that, McGregor will have little left. Boxing is like marathon ballroom dancing. Even though Mayweather hasn’t danced in a boxing ring in 23 months, he possesses muscle memory that goes back to when he was four-year-old. McGregor’s legs won’t be able to hold up against the athletically superior Mayweather over 12 rounds—or even six rounds.

McGregor, like Manny Pacquiao, is left handed. But unlike Pacquiao, when he met Money on May 2, 2015, McGregor is 29 and not shopworn. “Pac-Man” was 36 when he met Mayweather and dinged up quite a bit from his aggressive fighting style.

Will Saturday, August 26 be the night that Mayweather looks like a 40-year-old fighter? Will it show in his reaction time to McGregor’s assaults?

Money hasn’t stopped anyone since be knocked out Victor Ortiz (KO 4) on September 17, 2011—which will be almost six years when he steps in against McGregor. And even the Ortiz stoppage was dubious, considering Ortiz had head butted Mayweather and after being warned by referee Joe Cortez, approached Money with his hands down trying to apologize when Money legally slugged him.

McGregor has a two-inch reach advantage (74″ to 72″) and is bigger than Mayweather. In December 2015, McGregor nailed UFC featherweight (which is 145 pounds) champion Jose Aldo with a short, accurate left.

Could an unseen McGregor left rock the world Saturday, August 26?

It’s possible. But highly improbable.