The American, who won a record eight Olympic gold medals in Beijing last year, suffered his first defeat for five years last night when he was beaten into second place in the 200 metres freestyle by Germany's Paul Biedermann who was wearing a 100 per cent polyurethane Arena suit.

Bob Bowman, Phelps' coach, claimed that the suits, which have revolutionised the sport, should be banned immediately rather than next April or May, as the world governing FINA have announced.

He said: "The mess needs to be stopped right now.

"This move to April is unacceptable.

"It has to be January 1, if not, you know, next Monday.

"You can't trust what they [FINA] say.

"It might be never.

"My recommendation to him [Phelps] is not to swim internationally until this is resolved."

Phelps said: "He [Bowman] chooses what's right for me and what's right for my training.

"That's his decision."

Biedermann responded diplomatically to questions about the suit.

He said: "The suits make a difference of course.

"I think we're in a dangerous situation with what comes next.

"It's really important to go back to the real swimming.

"I hope there will be a time I can beat Michael Phelps without the suit of course and I hope that it could be next year or the next two years, but I also think it's not all about the suit."

FINA have held off on setting a date to implement the new swimsuit regulations, saying it needed to give a panel of scientists enough time to define the parameters and manufacturers enough time to adjust.

Steve Furniss, the founder of suit manufacturer Tyr, said: "As the old saying goes, we will not know where we are going until we arrive there, but even then we may not know where we are."

Francesco Fabbrica, the President of Jaked, the Italian manufacturer producing some of the controversial new suits, including one worn by Federica Pellegrini (pictured) when she set a world record for the 400m freestyle on Sunday ahead of British pair Jo Jackson and Rebecca Adlington, said his company does not need extra time and "now is ready for the next year, in this moment".

With a majority of swimmers at worlds wearing new suits made of materials such as buoyancy-enhancing, friction-reducing polyurethane, 15 world records have been set in the first three days and many race results have been shocking.

The FINA bureau, the organisation's decision-making board, decided that it agrees with a resolution passed last week by FINA members that restricts swimsuit material to permeable "textiles" (the full definition of which will be decided by the scientific panel) and outlaws full-body suits.

Men's suits will no longer be allowed to extend past the navel or knees.

Women's suits cannot go past the knees or cover the neck or shoulders.

Craig Brommers, senior vice president of marketing for swimsuit manufacturer Speedo, said: "We do believe that going back to 100 per cent textile bodysuits would have been the appropriate solution.

"It does seem an extreme step backwards."