Sun Yang, China's three-time Olympic gold-medal winner in swimming, who faces a ban of up to eight years for missing a doping test, told an appeal hearing on Friday that testers were at fault since they failed to prove their identity.

At a public hearing of the Court of Arbitration for Sport in Montreux, Switzerland, Sun defended his actions, blaming the testers for acting unprofessionally and ignoring protocol.

The 27-year old and his bodyguard are accused of smashing a vial containing his own blood sample with a hammer.

"If they had been professional and had shown their identification, we would not be here today," Sun said in Chinese, which was translated by court interpreters.

"The officials were not even capable of proving their identity. How could I allow them to take my sample?"

Sun said paperwork provided by the testers was invalid.

He added: "If a policeman came to your house in the middle of the night and said, 'I'm a policeman, but I don't have any identification,' how would you behave?"

A national idol in China, Sun was cleared of wrongdoing in January by FINA.

The international swimming federation admitted that Sun and a security guard had used a hammer to smash the vial during an out-of-competition test in September 2018.

They, however, agreed officials who came to conduct the test had not produced proper identification or followed protocol.

The World Anti-Doping Agency (WADA) appealed against the decision, demanding that a ban of two to eight years be imposed on the swimmer.

Representatives of the Swedish firm IDTM, which has been carrying out the tests on FINA's behalf since the 1990s, said Sun was given standard documents.

Sun participated in the World Championships in Gwangju, South Korea, in July after getting the clearance from FINA, where he won two gold medals.

Australia's Mack Horton, who came second in the 400-meter freestyle, refused to stand on the podium with him.

It was declared a ruling on Sun's case would not be issued on Friday but at a future date following deliberations at court.