Pacquiao and Mayweather have been unable to settle their differences
Manny Pacquiao's promoter Bob Arum says the proposed 'super-fight' with Floyd Mayweather Jr is off after talks failed to resolve the fighters' differences.
Pacquiao pulled out of the lucrative contest, which was scheduled for 13 March, after Mayweather demanded random drugs tests ahead of the bout.
A mediator was called in to settle the dispute but after two days the pair failed to resolve their differences.
"There is no chance ever of salvaging it for March," said Arum.
"I knew this was going to happen. There's no chance for it ever to happen," added Arum.
The 'super-fight' was likely to have been the richest in boxing history.
With potential purses of up to £25m per fighter acting as a strong incentive, former judge Daniel Weinstein, who had helped resolve previous spats between the pair, was brought in as a mediator.
The duo had previously agreed all points of the contract apart from the drug testing and were said to be close to a deal after the mediation, but subsequent discussions on Wednesday led Pacquiao's promoters Top Rank to declare the fight was cancelled.
"I've been saying this for years. He's a psychological coward who doesn't want to fight anybody who has a chance of beating him," added Arum.
Mayweather, 32, and Pacquiao were both happy to take unlimited urine tests but Pacquiao will submit to blood testing only on specific dates.
Last week he responded to claims that he had been using performance-enhancing substances by issuing a lawsuit against Mayweather, Mayweather's father and uncle as well as Golden Boy Promotions.
Oscar de la Hoya, founder of Golden Boy, was also mentioned.
Mayweather's team attempted to defuse the situation by issuing a statement last week in which they claimed they had not accused Pacquiao of anything.
Weinstein resolved a dispute three years ago over the promotional rights to Pacquiao, who had signed contracts with Top Rank and Golden Boy, who represent Mayweather.
Under the global settlement, Top Rank retained Pacquiao's promotional rights with Golden Boy receiving a percentage of Top Rank's profit from his future bouts.
Unbeaten Mayweather and five-weight champion Pacquaio - considered to be the best pound-for-pound boxers in the world - were set to meet at the MGM Grand Garden Arena in Las Vegas in the biggest fight since the turn of the century.
Pacquiao, 31, became a five-weight world champion following his WBO welterweight title win over Miguel Cotto in November, while Nevada-based Mayweather returned from a 21-month retirement to beat Mexican Juan Manuel Marquez in September.