BEIJING, Feb. 28 (Xinhua) -- The Chinese Swimming Association (CSA) was "deeply sorry" about the Court of Arbitration for Sport (CAS) decision to ban Olympic and world champion Sun Yang for eight years.

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

"We are deeply sorry  (the decision)," the CSA said in a statement. "The CSA has always held a zero-tolerance stance on doping and attached much importance to athletes' anti-doping education."

The CSA said as far as they knew, the international testing company IDTM fielded sample collectors "without professional training and eligible credentials" to conduct doping test on Sun in 2018.

After receiving the bad news, Sun said he would appeal to the Swiss Federal Tribunal against the decision.

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

WADA appealed to CAS in March 2019 after swimming federation FINA had ruled the doping sample collection at Sun's home was invalid.

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 IDTM on September 4, 2018, saying the Doping Control Officer and her assistants lacked sufficient authorization and credentials.

His case was later heard by 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 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.  ■