Floyd Mayweather Sr., father and trainer of Floyd Mayweather Jr., believes his son is going to make good on his promise of retirement in September, telling XM Radio - "he's done everything, he has nothing more to prove."

Last Saturday night in Las Vegas, Mayweather won a twelve round unanimous decision over Manny Pacquiao at the MGM Grand in Las Vegas.

"I told everyone he would whoop Pacquiao easy. He will never beat Floyd," Mayweather Sr. said.

After the match, Mayweather told media members that he planned to retire in September - which is the final fight on his exclusive Showtime/CBS contract.

But then three days later there was a ray of hope that a rematch was going to take place, when Mayweather sent a text message to reporter Stephen A. Smith and said he was willing to face Pacquiao in 2016 after the Filipino star recovered from shoulder surgery.

Mayweather's position quickly changed, after Pacquiao blamed the pre-existing right shoulder injury for his loss.

In Showtime interview, Mayweather branded Pacquiao a "sore loser" and a coward and now says he won't delay his planned retirement to grant the Philippine icon a rematch next year.

The 38-year-old says he couldn't detect any physical problem for Pacquiao during the bout, after which the Filipino and his camp said he was suffering from a right shoulder injury.

"Absolutely not," Mayweather said. "He was fast. His left hand was fast. His right hand was fast and he was throwing them both fast and strong."

Although Pacquiao had arthroscopic surgery to repair a torn rotator cuff in Los Angeles on Wednesday, Mayweather said his plea of injury was nonsense.

"He lost. He knows he lost. I lost a lot of respect for him after all of this," said Mayweather.

As to the flip-flop on a possible rematch, Mayweather said simply: "I change my mind.

"At this particular time, no, because he's a sore loser and he's a coward... If you lost, accept the loss and say, 'Mayweather, you were the better fighter.'"

Pacquiao, 57-6-2 with 38 knockouts, is expected to be out of the ring for nine months to a year.

With a victory in that fight against a still-to-be-named opponent, Mayweather would match Rocky Marciano's iconic 49-0 ring record.

He has insisted he would be happy to retire with that mark and wouldn't be tempted to stay around and try to make it a round 50 victories.