LAS VEGAS, Nevada – The July 18 fight between unbeaten Floyd Mayweather, Jr. and Mexico's Juan Manuel Marquez has been postponed after Mayweather injured a rib in training.

Mayweather had announced the bout on May 2, signalling an end to his 17-month absence from the ring hours before Filipino superstar Manny Pacquiao delivered a devastating knockout of England's Ricky Hatton.

The American, 39-0 with 25 knockouts, was to take on Mexico's Marquez in the same arena where he last fought, stopping Hatton in the 10th round in December 2007 to keep the undisputed welterweight title.

Once Pacquiao had so convincingly dispatched Hatton, it was clear that the Filipino was square in Mayweather's path if the American wanted to claim boxing's pound-for-pound throne.

Marquez was to have been the first step on that road for Mayweather.

"I am extremely disappointed that this fight has to be postponed," Mayweather said. "I was training very hard and looking forward to getting back in the ring on July 18th."

Marquez, the World Boxing Association lightweight champion, was to move up in weight for the bout.

"I was very disappointed to hear the news about the fight being postponed," Marquez said from his training camp in Mexico. "I will remain focused, in shape and ready to fight whenever the fight is rescheduled for."