DALLAS, (Reuters) – WBO welterweight champion Manny  Pacquiao should fight Floyd Mayweather Jr. and then retire later this year because there are no other legitimate contenders, according to the Filipino fighter’s trainer.

Talks for a March megafight with the undefeated Mayweather fell apart this year so Pacquiao agreed to fight lesser-known Joshua Clottey of Ghana today in Dallas, which may be the champion’s penultimate fight.

“There’s no more challenges out there,” Pacquiao’s trainer Freddie Roach, who trained 26 other world champions including Oscar De La Hoya and Mike Tyson, told reporters this week in Dallas.

“I would like to see him go out on top and not be one of those cases where he stays around too long. I know it’s an addictive sport, but what better way to go out than on top?”

Pacquiao, 50-3-2 (38 KOs), and Mayweather seemed certain to clash today in Las Vegas when Pacquiao beat Miguel Cotto for the WBO belt in November.

But negotiations collapsed over Mayweather’s insistence that Pacquiao submit to random blood tests, so Pacquiao turned to Clottey and Mayweather scheduled a fight with Shane Mosley.

“If Mayweather doesn’t come to the table, then who else is there?” he asked rhetorically. “I know there’s some fights out there, but will you guys really be interested and will the general public want to buy it?”

A Mayweather bout would mark the 23rd time Roach has worked in Pacquiao’s corner since their relationship began in 2001.

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Pacquiao had already won a world title by then — the WBC flyweight crown — and within weeks of training with Roach had added the IBF super bantamweight belt. He and Roach won five more titles and are one of boxing’s most successful tandems.

Even so, the trainer wants to protect his fighter and is adamant that he will urge Pacquiao to hang up the gloves.

Roach understands the dangers of staying in the sport too long as he suffers symptoms of Parkinson’s disease, the result of his own boxing career.

“People ask me: ‘He’s the guy you’ve made the most money from, why would you want him to quit?’,” said Roach.

“We’ve done well with each other and I’d rather see him quit than continue after a Mayweather fight. I just don’t see any point in going any further.”