MANILA, Philippines -- Five-time Trainer of the Year Freddie Roach said a fight between pound-for-pound kings Manny Pacquiao and Floyd Mayweather has to happen this year; otherwise, boxing fans will begin to lose interest.

"I think it has to happen in 2012, because people are starting to say, 'Who cares at this point?'" Roach said in an interview with Mario Diaz of WPIX.

"It is starting to lose momentum instead of gaining, so they better do it this year," he added.

Mayweather has recently taken to Twitter to challenge Pacquiao to a May 5 fight date, but the Filipino boxer would rather fight at the end of May for "economic reasons."

Pacquiao is also insisting on a 50-50 purse split.

Given the recent developments, Roach does not believe his fighter will face Mayweather in May.

"I definitely think it will be the second fight for both of them this year," he said. "I think they will both have one more fight, a tune-up fight."

If Pacquiao does not face Mayweather, he will choose to fight one of the following fighters: Juan Manuel Marquez, Miguel Cotto, Lamont Peterson or Timothy Bradley, Jr.

Mayweather, meanwhile, may face Robert Guerrero or Saul "Canelo" Alvarez on May 5.