Adam Peaty questioned China's relay victory on the final night of swimming at the Paris Olympics, saying "there's no point winning if you're not winning fair".
China took gold in a thrilling men's 4x100m medley relay race, beating the United States into second and France third, with the British quartet finishing fourth.
Two of the four gold medallists, Qin Haiyang and Sun Jiajun, were among the 23 Chinese swimmers who reportedly returned positive doping tests prior to the Tokyo Olympics.
They were not banned because the China Anti-Doping Agency determined they had unintentionally ingested the substance because of contamination.
"If you touch and you know that you're cheating, you're not winning, right?" said Peaty, who has won three gold and three silver medals for Team GB over his Olympics career.
"I don't want to paint a whole nation or group of people with one brush, I think that's very unfair.
"To the people that need to do their job - wake up and do your job."
Details of the China case were first made public by the New York Times in April, which shared reporting with German broadcaster ARD. The positive tests in 2021 were not made public at the time.
The World Anti-doping Agency (Wada) said it was "not in a position to disprove" the conclusion made by the Chinada and opted not to appeal after consulting independent experts as well as external legal counsel.
An independent report has since found Wada did not show bias in its handling of the case and Chinese athletes were drug tested up to twice as much as other athletes in the run up to the Paris Games.
In its initial report, the New York Times also said Qin, who won three breaststroke titles at the World Championships last year, had previously tested positive for another substance.
Although it did not name Qin, 25, specifically, Wada said the levels were below the current threshold for reporting and came from eating contaminated meat.
Peaty, 29, added: "One of my favourite quotes I've seen lately is that there's no point winning if you're not winning fair.
"I think you know that truth in your heart.
"For me, if you've been on that and you have been contaminated twice, I think as an honourable person you should be out of the sport. But we know sport isn't that simple."
Following the allegations, the row spread as the United States Anti-Doping Agency (Usada) chief executive Travis Tygart suggested a cover-up - a claim Wada rejected as "completely false and defamatory".
A criminal investigation is under way in the US over the issue, while a different report into World Aquatics' handling of the case also found there was no mismanagement or cover-up.
"We have to have faith in the system but we also don't," said Peaty, who lined up with Ollie Morgan, Duncan Scott and Matt Richards.
"The Americans have been very vocal. We didn't want to get distracted with that.
"But I think it's got to be stricter. What I've said from the start is that it's fraud. If you're cheating, it's fraud."
Peaty was swimming after what he said was the "worst week" of his life physically. He tested positive for Covid-19 on Monday, a day after taking silver in the 100m breaststroke event.
He did not commit to his future in the sport after the relay, but said "it could have been" his last swim.
"I don't know what the answer is," he added.
Elsewhere, the US set a new world record in the women's 4x100m medley relay, beating great rivals Australia into silver to pip them to topping the swimming medal table for most golds.
The Americans leave the pool with eight from 28 medals, while Australia end with seven golds and 18 overall.
One of those American golds came in the final individual race as Bobby Finke broke the world record to successfully defend his 1500m freestyle title.
He led from the gun to win in 14 minutes 30.67 seconds, taking the record held by Sun Yang – the Chinese swimmer who was given an eight-year doping ban in 2020. Ireland's Dan Wiffen took bronze, his second medal of the week after gold in the 800m freestyle.
The star of the meet has undoubtedly been Leon Marchand. He was part of the French relay team beaten by China, but the third place means he adds bronze to his haul of four individual golds.
Sweden's Sarah Sjostrom completed the freestyle sprint double by adding the 50m title to the 100m crown she won earlier in the meet.
Team GB finished with five medals – the 4x200m freestyle relay their only gold, having set a target of beating or equalling the eight medals won in Tokyo at the previous Games.
For the first time since 2004, no British women were on the podium.
