Floyd Mayweather celebrates the unanimous decision victory in his welterweight unification championship bout against Manny Pacquiao, in Las Vegas, Nevada, in May 2015Floyd Mayweather celebrates the unanimous decision victory in his welterweight unification championship bout against Manny Pacquiao, in Las Vegas, Nevada, in May 2015 (AFP Photo/Al Bello)
Las Vegas (AFP) - Floyd Mayweather may insist Saturday is his last fight in a stellar career, but his welterweight rivals are hoping they will still get the chance to dethrone the pound-for-pound king.
And they warned that the Las Vegas showdown against massive underdog Andre Berto just might not be the cakewalk that many fans and pundits have predicted.
Mayweather, 38, faces Berto -- who has three losses in his last six fights -- at the MGM Grand Garden Arena striving to equal the perfect 49-0 record of heavyweight legend Rocky Marciano.
The unbeaten American insists it will be his swan song, the crowning moment of a glittering 19-year career as the best boxer of his generation.
But critics accuse him of bigging up the retirement talk to flog a fight that barely 24 hours away had failed to sell out.
The exciting and unbeaten Keith Thurman (26-0, 22 KOs) said: "This might be the last performance. How eager is Floyd to make a statement and show the world that he is an entertaining fighter?
"I'm here for the mystery factor: Is this his last fight or not?"
The unbeaten Danny Garcia -- who like Thurman has designs on a Mayweather match-up -- said: "I don't think it's going to be his last fight.
"As I said before: If he has to pay taxes on that $250 million (in earnings) we are going to see him next year right back in the ring.
"Floyd's a rich man and has made a lot of money. He knows what he's doing."
Shawn Porter (26-1-1, 16 KOs), who could face the fearsome Thurman later this year, warned Berto, 32, has youth on his side against Mayweather.
"People are overlooking that he is younger and he has some speed and quickness," said Porter, who nevertheless said he had been looking for evidence that Mayweather is slowing up -- but had not found any.
"He still looks spectacular and he still looks great in every fight.
"That said, it's going to be a much more competitive fight than people anticipate."
- 'Mayweather in seventh' -
Thurman, one of the most explosive talents in modern-day boxing, agrees.
"A lot of people who fight Floyd fade in the late rounds," said Thurman.
"The first four rounds Berto needs to try catch him off-guard because it takes time for Floyd to figure you out.
"He needs that time but it's in that time that he's most vulnerable.
"Berto has nothing to lose with a loss. If Mayweather loses he loses everything."
Garcia (31-0, 18 KOs) said the underdog's best chance would be catching the champ with a big shot.
"But if Floyd goes in there and is Floyd, then I think he can probably stop Berto," said Garcia.
"I think it'll be about seventh round. Floyd will probably stop him."