Floyd Mayweather may have been gracious in the lead-up and in the immediate aftermath of his unanimous decision welterweight title victory over Manny Pacquiao last Saturday night, but it apparently didn’t last.

In an exclusive interview with Jim Gray that is scheduled to premiere Saturday at 9 p.m. ET on Showtime, the pound-for-pound king calls Pacquiao a “sore loser” and a “coward” and backtracked on reports that he would be interested in a rematch with the Filipino star.

Floyd Mayweather now says he's 'lost a lot of respect' for Manny Pacquiao. (AP) More

“Did I text [ESPN’s] Stephen A. Smith and say I will fight him again?” Mayweather told Gray. “Yeah, but 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.’ ”

At the heart of Mayweather’s discontent with Pacquiao is his right shoulder injury, which was reported by Yahoo Sports immediately after the megafight at the MGM Grand in Las Vegas. Pacquiao talked about the injury in the post-fight news conference and said it limited him in the bout but that he didn’t want to use it as a reason for the loss.

“Excuses, excuses, excuses,” Mayweather said. “I’m not going to buy into the [expletive] and I don’t want the public to buy into the [expletive]. He lost. He knows he lost. I lost a lot of respect for him after all of this.”

Pacquiao underwent shoulder surgery Wednesday to repair a torn rotator cuff and is expected to be out nine-to-12 months.

Mayweather improved to 48-0 in the richest and most financially successful fight in boxing history and is slated to fight again in September, but whom he will face remains a topic of discussion.

In the meantime, we’ll wait and see if the champ also changes his mind about giving up all of those title belts.