WBO welterweight world champion Manny Pacquiao on Friday kept alive hopes for a rematch with Floyd Mayweather, saying the epic clash was "possible" but only if his arch rival returns to the ring.

The Filipino icon, 37, made a winning comeback from his brief retirement in November following his defeat to Mayweather last year in the richest fight in boxing history.

"If he will come back in boxing, there is a possible that there is a rematch, but right now we don't talk or discuss about it," Pacquiao told reporters in Tokyo, where he will open his first overseas boxing gym next year.

Asked if he is confident about winning a rematch, Pacquiao said only: "Yes, of course."

Pacquiao originally retired in May after beating American Timothy Bradley in a non-title fight before standing for and winning a seat in the Philippines Senate.

"I feel lonely and sad because I (was) no longer active in the sport that I love," Pacquiao said.

"I can still fight and my body is still okay, so I decided to come back and I'm here." 

Pacquiao fuelled talk of "Pacquiao-Mayweather 2" when he invited the undefeated American, who retired in September 2015, to attend his successful comeback against Jesse Vargas in Las Vegas on November 5.

Earlier this month, Pacquiao teased fans about a possible rematch by posting pictures on social media wearing a suit bearing photos of him and Mayweather in the lining. 

But Mayweather, 39, said days later he had no plans to come out of retirement. 

Meanwhile, organisers of Friday's event told reporters there would be no "political" questions asked of the boxer-cum-senator.

Despite admitting to past use of illegal substances, Pacquiao has endorsed Philippine President Rodrigo Duterte's high-profile war on drugs.

The crackdown has left more than 4,000 people dead since  the president took office in June and has been condemned by the United Nations.

Source: AFP