NEW YORK, US - Manny Pacquiao has satisfied Floyd Mayweather's demands that he state his desire to fight the American, but that still may not be good enough to make the mega-fight, boxing promoter Bob Arum said on Thursday.

Arum said Filipino Pacquiao, who won the WBO welterweight title last Saturday for his seventh world title in an unprecedented seventh weight class, told a radio interviewer this week he wanted to fight Mayweather in what would be a showdown between the world's two best pound-for-pound boxers.

"But you have to understand Mayweather's psyche," Arum told reporters at a lunch saluting Yuri Foreman, who became the first Israeli to win a world title when he claimed the WBA super welterweight crown on the Pacquiao undercard.

"Psychologically he may not be prepared to do this fight.

"Now this is me being an amateur psychologist, but Mayweather is so tied up with the fact that nobody has beaten him, that he has a zero on his record, that I don't know if he would be willing to go into the ring with anybody that could jeopardise that zero," added Arum, who is Pacquiao's promoter.

The 32-year-old Mayweather, who has won titles in five different weight classes, has a 40-0 career record while Pacquiao, 30, improved to 50-3-2 when he stopped Miguel Cotto in the 12th round in Las Vegas.

"He (Mayweather) is afraid, terrified of losing that zero," said Arum, possibly in an effort to goad Mayweather into making the match.

"That's why he's ducked (Shane) Mosely, (Antonio) Margarito and Cotto, and the question is will he duck Manny Pacquiao because he's so afraid of losing that zero."

Representatives of HBO Boxing expressed confidence that a Pacquiao and Mayweather would fight as welterweights in May, and Arum said he would try his best to arrange it.

"Boxing is on such a roll now, not to do this fight would slow down considerably the momentum that boxing has, and that would be wrong," said Arum.