Former welterweight champion Andre Berto believes if UFC superstar Conor McGregor pulls off the upset over Floyd Mayweather - the sport of boxing would suffer a big blow.

This coming Saturday night at the T-Mobile Arena in Las Vegas, McGregor will make his professional boxing debut against Mayweather, who is 40 years old and coming back to the ring after two years in retirement.

Mayweather retired back in September 2015 - and person he defeated was Berto, by way of a twelve round unanimous decision.

Berto is caught in the middle of this fight.

He's loyal to boxing, but he's also close friends with McGregor. Berto's brother Edson and sister Revelina are MMA fighters, and his father Dieuseul fought at UFC 10.

Besides boxing taking a hit, Berto also says Floyd's legacy would take a big blow as well - with suffering his first career defeat in 50 fights.

McGregor, who is currently the biggest star in mixed martial arts, has very little boxing experience and is pegged as a tremendous underdog in the fight.

“If this were to be an upset, it would definitely be a big blow to the boxing game, for sure,” Berto told The MMA Hour. “Definitely, definitely. It’s gonna be a big blow to Floyd’s legacy, as well. Just being undefeated and able to let some guy upset you and he’s an MMA fighter and he probably talks a little more shit than you talk. It’s gonna be tough for him to swallow if that happens.”

“It’s gonna be a real tough pill to swallow for the boxing game. Especially for one of our top, top guys — probably one of the best in the game. That would be a tremendous pill to swallow. Of course, like I said, we’ve been going back and forth with the whole MMA thing for a long time. Boxing and MMA. I was able to grow up with both. I just love combat sports in general. But if he takes the L, it would definitely be a huge blow to [boxing], for sure.”