By Edward Chaykovsky

On September 12th at the MGM Grand in Las Vegas, WBC/WBA welterweight champion Floyd Mayweather Jr. (48-0, 26KOs) will step in the ring for what he claims is the last time of his 19-year career.

There are many who are doubting Mayweather's words. They believe the fighter will return next May to chase his 50th pro win - which in turn would break the 49-0 record of legendary heavyweight Rocky Marciano. 

The fight with Berto will be the final bout of Mayweather's exclusive contract with Showtime/CBS.

There have been industry rumors that CBS/Showtime have attempted to sign Mayweather to a three fight extension - if the boxer decides to continue his career in the future.

Mayweather gave a borderline confirmation of those talks, but continues to stand firm on his planned retirement.

"They say they'll offer me a lot of money" to keep fighting, Mayweather said. "I have a lot of money. I'm OK. ... It's the end of my [Showtime] deal. I'm an old man now. I'm 38."