Five division world champion Floyd Mayweather Jr. believes the critics are underestimating and overlooking his upcoming opponent, UFC superstar Conor McGregor.

At 40 years old, Mayweather will break a two-year retirement on August 26th, when he faces McGregor in a Showtime Pay-Per-View from the T-Mobile Arena in Las Vegas.

McGregor is a tremendous underdog and given zero chance of victory by most experts. He's never had a single professional boxing match and now he's facing one of the best defensive boxers in the history of the sport - and they will wear 10 ounce gloves at the junior middleweight limit of 154-pounds.

Mayweather views the bout with McGregor as a very dangerous situation.

McGregor has lost three times in MMA, but Mayweather points out that his next opponent has never been beaten on his feet. All three defeats came by submission. 

"I'm just thankful for being in this position; to be able to be at this age [40] and still be competing against guys in their 20s. It's a blessing, but if you look at it on paper, everything leans toward him [McGregor] on paper. He's bigger, he has a 74-inch reach, I have a 72-inch reach. I'm inactive. He's active. Youth is on his side. He's in his 20s, I'm in my 40s," Mayweather explained.

"He's a stand-up fighter. We've never seen him lose standing up, so he can fight standing up. That's one thing he can do. He feels like he's the best. When I was competing I was the best. So I had to come back for this last hurrah."

Win or lose, Mayweather has no intention of fighting beyond this contest and made that clear to his adviser, Al Haymon.

"I gave Al Haymon my word. I shook his hand, gave him a hug. I promised him, I gave him my word [about retiring]. He said, 'Son, you don't want for nothing.' I own so much property, made so many smart investments. It's truly a blessing," Mayweather said.