London - Triple world champion Adam Peaty says China's Sun Yang got off lightly for last year's doping offence and the Briton fears being beaten by a non-clean swimmer at the Rio Olympics next year.
Peaty won the 50m and 100m breaststroke titles at the Kazan world championships as well as the 4x100m mixed medley and is tipped to become Britain's first male Olympic swimming gold medallist for 28 years.
Despite his golden haul, Peaty was beaten to the "male swimmer of the meet" award in Kazan by 23-year-old Sun, who won the 400m and 800m freestyle titles and was second in the 200m but pulled out of the 1 500m final minutes before the race, saying he "didn't feel good in my heart".
Sun served a three-month ban imposed by the Chinese Swimming Association last year for taking a banned stimulant, but Peaty says that sent out the wrong message.
"I don't know what's gone on behind the scenes," Peaty, world record holder in the 50m and 100m breaststroke, told the BBC. "But it's disappointing to see that he was let off so cautiously - it's like a slap on the wrists.
"It's not a good message - this is not (just) Sun Yang, it's doping as a whole.
"People out there now will be thinking 'if I can dope and not get caught then why am I doing it the hard way?'"
Peaty said he was tested "seven or eight times" during the championships as he helped Britain to its best ever total of nine medals at the championships.
"All I can do is improve my times and hope I don't come second to someone who dopes," he said.