China’s star swimmer Sun Yang is preparing to give evidence in a landmark public hearing where he risks being banned from the 2020 Tokyo Olympics.

Sun is the first witness scheduled to speak at 9.15 a.m. Swiss time (0815 GMT) in a rare Court of Arbitration for Sport appeal hearing held in open session before media and public observers.

The three-time Olympic champion’s hearing is expected to last more than 11 hours. A verdict from three CAS judges is unlikely this year.

The appeal case was brought by the World Anti-Doping Agency. It centers on Sun’s right to refuse cooperation with three anti-doping officials who tried to take blood and urine samples at his home in China last year.

A security guard instructed by Sun’s mother used a hammer to smash a box containing a vial of his blood during a late-night dispute after the swimmer questioned the collection team’s credentials.

A first judgment in January saw Sun only cautioned by a tribunal appointed by world swimming body FINA.

Though Sun and his entourage were criticized for their conduct, the tribunal panel said the sample mission was void and invalid because anti-doping protocol was not followed. Technically, Sun was judged to be not properly notified of needing to give samples.

WADA has asked for a ban of between two and eight years believing Sun voluntarily refused to submit to give samples.

If WADA’s appeal is upheld, Sun risks a longer sanction because it would be his second offense. He served a three-month ban imposed by Chinese authorities in 2014 after testing positive for a banned stimulant.

Sun became a star in China as its first man to win an Olympic title in swimming.

He took gold medals in 400 and 1,500 meters freestyle at the 2012 London Olympics. He added gold in 200 at the 2016 Rio de Janeiro Olympics.

Sun also has 11 world championships titles and is a polarizing figure in the sport.

He provoked anger among rivals by winning two titles in July while the CAS appeal was pending. Medalists from Australia and Britain refused to stand on the podium with him in Gwangju, South Korea.

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