A top US coach Monday called China's Ye Shiwen "suspicious" and compared her to East Germany's drug-addled athletes after her super-fast times were questioned at the London Olympics.
John Leonard, executive director of the World Swimming Coaches Association, told The Guardian that the 16-year-old's lightning freestyle leg in her world-record 400m individual medley swim was simply "impossible".
The schoolgirl timed 58.68sec in the last 100 metres, a whisker off US winner Ryan Lochte's time in the men's competition. Astonishingly, her final lap was quicker than the American champion.
"The one thing I will say is that history in our sport will tell you that every time we see something, and I will put quotation marks around this, 'unbelievable', history shows us that it turns out later on there was doping involved," Leonard told the British newspaper.
"That last 100m was reminiscent of some old East German swimmers, for people who have been around a while. It was reminiscent of the 400m individual medley by a young Irish woman in Atlanta."
Leonard was referring to Michelle de Bruin, who emerged as a triple gold-medallist at the 1996 Games but was banned for four years in 1998 for tampering with a urine sample.
"Any time someone has looked like superwoman in the history of our sport they have later been found guilty of doping," he said, adding: "I have been around swimming for four-and-a-half decades now.
"If you have been around swimming you know when something has been done that just isn't right. I have heard commentators saying 'well she is 16, and at that age amazing things happen'. Well yes, but not that amazing. I am sorry."
Ye, whose gold medal swim was described as "insane" by former record-holder Stephanie Rice, has already denied foul play. Late on Monday, she set the world's fastest time in the 200m individual medley semi-finals.
"There is no problem with doping, the Chinese team has a firm policy so there is no problem with that," said the youngster.
Ye won the 200m medley at the world championships last year, but her 400m medley swim shaved seven seconds off her time at that meet. Leonard admitted such an improvement was possible at her age.
"But the final 100m was impossible. Flat out. If all her split times had been faster I don't think anybody would be calling it into question, because she is a good swimmer," he said.
"But to swim three other splits at the rate that she did, which was quite ordinary for elite competition, and then unleash a historic anomaly, it is just not right."
He added: "No coach that I spoke to yesterday could ever recall seeing anything remotely like that in a world level competition.
"Where someone could out-split one of the fastest male swimmers in the world, and beat the woman ahead of her by three-and-a-half body lengths. All those things, I think, legitimately call that swim into question."
Leonard is the first coach to speak out about Ye. British media have also pounced on her performances, pointing to China's record of state-sponsored doping in the 1980s and 1990s.
"Ye's amazing time for freestyle leg scarcely credible," read a headline in The Times, which noted that the youngster was a former team-mate of Chinese swimmer Li Zhesi, who was barred from the Olympics over blood-booster EPO.
"Chinese swimming has such a shameful history of doping that any remarkable achievement by one of its athletes is inevitably met with cynicism," remarked the Daily Telegraph.
But Arne Ljungqvist, medical commission chief for the International Olympic Committee, called the speculation "sad."
"For me, it is very sad that an unexpected performance is surrounded by suspicions," he told a briefing.
"I mean to raise suspicion immediately when you see an extraordinary performance -- to me it is against the fascination of sport."
And Frank Busch, national team director for USA Swimming, compared Ye to Jamaica's Usain Bolt, who surprised the world by winning three track sprint titles in world record times at Beijing 2008.
"I don't know what the Chinese are doing. But I don't think anybody saw Usain Bolt running that fast in 2008. There are times you have phenoms coming up that surprise you with what they can do," he told the New York Times.
China, who only won one swimming gold at Beijing 2008, took two on the first two days in London through Ye and men's 400m freestyle winner Sun Yang.