Andre Berto will go into his welterweight title fight against Floyd Mayweather in Las Vegas next week as a heavy underdog but also as a man "on a mission" as he bids to end his fellow American's perfect 48-0 record.

Berto, 31, he has blinkered himself from all the hype and hoopla that usually surrounds the build-up to a Mayweather bout and claims he has never been fitter as he prepares to step into the ring at the MGM Grand Garden Arena on Sept. 12.

"I've had a tremendous training camp, a long camp but a tremendous camp," twice former welterweight world champion Berto told reporters on a conference call on Tuesday. "I've never run harder. I'm definitely in the best shape that I've ever been in.

"I've worked with a lot of different sparring partners. Floyd is a very skilled fighter but I think I bring a combination of speed and power to the table. I think I have a better athletic ability. I can keep up with Floyd."

Mayweather, widely regarded as one of the best defensive fighters ever, will put his unbeaten record on the line against Berto, a man who has lost three of his last six fights and is viewed by some as an easy opponent for their welterweight clash.

Should five-division world champion Mayweather win the WBC and WBA welterweight title bout as expected, in what he has said will be the final fight of his career, he would match the 49-0 record of former heavyweight great Rocky Marciano.

"It would be something huge, not just for me but for the sport," Berto said, when asked how much value he would place on a surprise victory over Mayweather.

"Floyd has been an icon for quite some time now and he's on his way to try to match a record. So for me, being the gym-hungry fighter coming in to take that away from him, that would be huge."

Mayweather, who improved to 48-0 by beating Manny Pacquiao in a 'mega-fight' in May that took five years to finalise and became the richest bout in boxing, is known for his trash talking and his flamboyant approach to life outside the ring.

Berto, however, prefers to leave all the hype to others while preparing for fights.

"I don't get caught up in all that," said the American, who has a 30-3 record with 23 knockouts. "I don't get caught up in all the hoopla and all the crazy shit.

"I don't want to get caught up and caught off guard. I'm on a mission."