The World Anti-Doping Agency wants China's star swimmer Sun Yang banned for up to eight years for alleged doping rules violations.

The Court of Arbitration for Sport said Tuesday ahead of a rare appeal hearing in open court on Friday that WADA requests a ban of two to eight years. Sun served a three-month ban in 2014 for a positive test.

If WADA wins, the three-time Olympic freestyle champion will miss the 2020 Tokyo Games.

WADA has challenged world swimming body FINA's ruling to merely warn Sun after a disputed attempt by sample collectors to take blood and urine from him at his home in China in September 2018. The late-night confrontation lasted from 11 p.m. to beyond 3:30 a.m.

The day-long hearing will examine why a secure box storing a glass vial of blood came to be destroyed by Sun's entourage, who questioned the sample team's authority. A FINA tribunal panel agreed the officials lacked proper credentials to make the sample collection valid.

WADA believes Sun broke anti-doping rules by refusing to submit to a sample collection.

All sides agreed to Sun's request to hold a first CAS appeal in public for 20 years. A verdict is unlikely until early next year.