In this July 21, 2019 file photo, Sun Yang of China celebrates after winning the men's 400m freestyle final at the Gwangju 2019 FINA World Championships in Gwangju, South Korea. (LI GANG / XINHUA)

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

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

The CAS upheld on Friday 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 that the doping sample collection at Sun's home was invalid

WADA had appealed to CAS after swimming federation FINA had ruled that 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.

Sun was found guilty of refusing to complete a doping test conducted by the international testing company IDTM on September 4, 2018, although he argued that the Doping Control Officer and her assistants lacked sufficient authorization and credentials.

Matthieu Reeb, General Secretary of the Court of Arbitration for Sport, CAS, speaks to journalists during a statement as he announces the decision taken in the arbitration procedure of the case of Chinese swimmer Sun Yang in front of the Court of Arbitration for Sport (CAS) in Lausanne, Switzerland, Feb 28, 2020. (JEAN-CHRISTOPHE BOTT / KEYSTONE VIA AP)

"In particular, the Panel found that the personnel in charge of the doping control complied with all applicable requirements as set out in the ISTI (International Standard for Testing and Investigation)," the CAS said.

"More specifically, the athlete failed to establish that he had a compelling justification to destroy his sample collection containers and forego the doping control when, in his opinion, the collection protocol was not in compliance with the ISTI."

The statement added that it was "one thing, having provided a blood sample, to question the accreditation of the testing personnel while keeping the intact samples in the possession of the testing authorities.

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"It is quite another thing, after lengthy exchanges and warnings as to the consequences, to act in such a way that results in destroying the sample containers, thereby eliminating any chance of testing the sample at a later stage."

Sun 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.

CAS ruled that Sun's world championship results should stand because he passed doping tests before and after the aborted 2018 control.

Sun's case was first 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 to the CAS.

READ MORE: DCA in Sun Yang case was 'construction worker'

As requested by Sun, the CAS held only its second public hearing in November 2019, which was marred by poor translation. The CAS was forced to ask all parties to submit written transcript of proceedings, including a full translation of Sun's testimony.