LONDON (GUARDIAN) - Floyd Mayweather has said he has only one more fight left before he retires and he will relinquish all five of his title belts in the next few weeks after beating Manny Pacquiao in a fight many had cast as the biggest in boxing history.

With the points win the American had unified three of the major welterweight titles and vanquished a foe many said he had spent years avoiding to preserve his undefeated record.

Mayweather said that he will fight again but that his next bout - in September, the last in a six-fight, 30-month contract with Showtime and CBS worth a potential US$250 million (S$333 million) - will be his last.

It is unclear who Mayweather's next opponent will be. Amir Khan, so often a bridesmaid in the sweepstakes, will be an odds-on favourite should he shine in an upcoming test against Chris Algieri.

Keith Thurman and Danny Garcia are potential names under the Premier Boxing Champions series controlled by Al Haymon, Mayweather's long-time adviser and the behind-the-scenes architect of the financial model behind the fighter's rise to the world's highest-earning athlete.

It has been reported Mayweather will fight a rematch with Miguel Cotto, the hugely popular Puerto Rican who last year stopped a shopworn Sergio Martinez for the lineal middleweight championship.

Their highly lucrative first meeting was Mayweather's sternest examination in years, which means he actually lost a few rounds before winning a comfortable decision.

Between Cotto's huge following of Puerto Rican fans and the opportunity for Mayweather to collect a championship in a sixth different weight division, it makes perfect sense.

"He's fought pretty much all the guys that's around here," Mayweather's father and trainer said. "All the hard-hitters. There's nothing left to do. My son needs to take this contract and end it. He's out of tough fights. He ain't got nothing left to prove."