WASHINGTON (AFP) - Floyd Mayweather said on Wednesday that he is more likely to end up in movies than keep boxing, as he rounded on his critics ahead of what he insists will be his last fight.

The unbeaten pound-for-pound king takes on massive underdog Andre Berto on September 12 in Las Vegas in a welterweight world title fight that has so far failed to capture the public imagination.

The American, 38, will make it 49-0 with victory - equalling the record of heavyweight legend Rocky Marciano - and has consistently said he will hang up his gloves afterwards. Few believe him.

In a conference call with reporters, Mayweather and Leonard Ellerbe, chief executive of Mayweather Promotions, said there had been "signficant" entertainment offers for the champion for when he calls it quits - including three "major" movie possibilities in the last week alone.

"I've been approached on numerous occasions (to act) but I'd rather be behind the scenes. I've had my time to shine," said Mayweather, who is not taking acting classes, reiterating Berto would be his last bout.

Fight fans and pundits have hit out at Mayweather's choice of Berto (30-3), who has lost three of his last six fights.

"When you are in my shoes, they are always going to criticize," said Mayweather.

"I couldn't care less. Nobody is forced to watch. Watch if you want to watch, don't watch if you don't want to watch.

"Write about it if you want to write about it, if you don't want to write about it, don't."