MANILA, Philippines - Putting together a mega-fight between top pound-for-pound fighters Manny "Pacman" Pacquiao and Floyd Mayweather Jr. is the number one priority of Top Rank chief executive officer Bob Arum.

In an interview with Boxing Talk, Arum confirmed that "Floyd Mayweather is our first priority. We want Manny to fight Floyd."

Arum said that he is already talking to investors who are interested in financing what would be the biggest fight in boxing.

A Pacquiao-Mayweather fight has long been considered to be the most lucrative bout in the sport. Many sports analysts say it stands to break numerous records, including live gate receipts, pay-per-view buys, and fighters' purses.

But Arum says they have a "Plan B" in case the Mayweather bout does not push through.

"If Floyd isn't available or the negotiations fall through, we will go after Juan Manuel Marquez," he said.

Mayweather has called on Pacquiao to sign a contract for the mega-fight, which he says should be held on May 5, 2012 at the MGM Grand Garden Arena in Las Vegas.

"May 5th is the date," Mayweather said.

Pacquiao has confirmed that negotiations are ongoing, but says nothing has been finalized. The Filipino boxer did say that he hopes Mayweather will be his next opponent.

In an ESPN interview, Arum also responded to criticisms from Pacquiao's strength and conditioning coach, Alex Ariza, who has accused the promoter of blocking the mega-fight.

"It was ridiculous. Ariza isn't the brightest bulb on the block. He has nothing to say about anything," Arum said. "I just called Freddie Roach and told Freddie to shut him up."