Mayweather mocks Pacquiao on Instagram; boxing fanatics call it 'cowardiness'...

MANILA, Philippines -- In response to Manny Pacquiao's call out, Floyd Mayweather Jr. posted an Instagram video to answer the Filipino champion's challenge.

The clip showing Juan Manuel Marquez decking Pacquiao and eventually knocking out the Filipino boxer was his rebuke against the eight-division champion's outright challenge to Mayweather.

The clip was uploaded just days after Pacquiao's lopsided win against New York's Chris Algieri.

The Filipino dynamo sent Algieri tumbling around six times before securing an easy unanimous decision win to retain the WBO welterweight title.

Immediately after his win, Pacquiao made it clear that he's pursuing Mayweather.

"The fans deserve that fight. It's time to make that fight happen," he said.

His promoter Bob Arum said back-channel negotiations are being done to arrange the fight, which could be the most lucrative in boxing history.

Arum said CBS, which owns Showtime, has already been meeting with HBO executives and Mayweather's camp to produce the super bout.

Arum, however, admitted that it would take Mayweather's cooperation for the fight to materialize.

"Just answer the phone," he told Mayweather. "There's no excuses this time."