Mack Horton of Australia (Center), Sun Yang of China (Left) and Gabriele Detti of Italy pose with their medals during the Men's 400m Freestyle Victory Ceremony in Rio de Janeiro, Brazil on August 6, 2016. [Photo/Agencies]

Sun was banned three months in 2014 for testing positive for trimetazidine which he used to treat his heart problem for years and failed to report for a theraputic exemption to the anti-doping authorities when the drug was put in the WADA banned substance list in 2014.

I used the words drug cheat because he tested positive," he said. "I just have a problem with athletes who have tested positive and are still competing."

Horton's hostility already showed early in the practice when Sun tried to greet him and Horton ignored and later told reporters "Sun splashed me to say hello, and I didn't respond because I don't have time for drug cheats."

Sun defended himself and said he would ignore Horton's "trick".

"I am clean. I think every single athlete who is able to compete at the Olympic Games deserves respect. It is unnecessary to disturb an opponent with such little tricks," he said.

Australian swimming is looking to save their image following a disappointing show at London 2012 when they didn't bring home a single individual gold for the first time since 1976.

It was later found out that members of the swimming team took the sleeping tablet at a pre-Games camp and star Grant Hackett is reported to seek treatment last year for addiction to the prescription drug zolpidem, sold as Stilnox in Australia.