BEIJING - Chinese swimmer Sun Yang said he will "definitely" appeal to the Swiss Federal Tribunal against the Court of Arbitration for Sport (CAS) decision to ban him for eight years.

"This is unfair. I firmly believe in my innocence," Sun told Xinhua. "I will definitely appeal to let more people know the truth."

The CAS upheld an appeal by the World Anti-Doping Agency (WADA), ruling that Sun had refused to cooperate with drug sample collectors during a controversial visit to his home in September 2018.

WADA had appealed to CAS after swimming federation FINA had ruled the doping sample collection at Sun's home was invalid.

"The appeal filed on 14 February 2019 by the World Anti-Doping Agency against the decision issued on 3 January 2019 by the Doping Panel of the Federation Internationale de Natation is upheld," CAS said in its ruling.

"Mr Sun Yang is sanctioned with an 8 (eight) year period of ineligibility, commencing on the date of the present arbitral award," it added.

The CAS held only the second public hearing in November 2019 after WADA appealed against FINA's decision that Sun was not guilty of anti-doping violations.

The hearing was marred by poor translation and the CAS was forced to ask all parties to submit written transcript of proceedings, including a full translation of Sun Yang's testimony.

Sun refused to complete a doping test conducted by the international testing company IDTM on September 4, 2018, saying the Doping Control Officer and her assistants lacked sufficient authorization and credentials.

His case was later heard by swimming's world governing body FINA, who decided on January 3 2019 that the swimmer was not guilty of anti-doping rule violations. WADA disagreed and appealed the decision. Then Sun asked for a public hearing.

Sun Yang won gold in the 200m freestyle at the 2016 Rio Olympic Games, as well as the 400m and 1,500m freestyle at the 2012 Olympics in London. The 28-year-old also claimed 200m and 400m freestyle titles at the 2019 FINA World Championships in Gwangju, South Korea.