Citing doping control procedures that it said were not properly followed, the Chinese Swimming Association has backed swimmer Sun Yang's appeal of an arbitration court's decision banning him from competition for eight years over a controversial drug test.

Sun, a three-time freestyle Olympic champion, was given an eight-year suspension from competition on Friday by the Lausanne, Switzerland-based Court of Arbitration for Sport. It said Sun was in violation of doping control rules by rejecting a random drug test conducted by International Doping Test and Management on Sept 4, 2018 in his home city Hangzhou, Zhejiang province.

Following the decision that could end his celebrated career, Sun reiterated his innocence in a social media post. He said he had only refused to complete the test over questions about the testers' eligibility, and he is ready to appeal to a higher court.

"I was shocked by the CAS decision, which I feel angry about and couldn't understand," Sun posted on his Weibo account on Friday evening.

"I have asked my lawyer to appeal the suspension to the Swiss Federal Tribunal. I firmly believe in my innocence. The truth will prevail over lies."

The arbitration court's verdict was result of a Nov 5 public hearing.

Participating were Sun, the Federation Internationale de Natation or FINA, which is swimming's world governing body, and the World Anti-Doping Agency. It followed WADA's appeal of an earlier FINA ruling that cleared Sun of any wrongdoing during a conflict over Sun's sample collecting procedure.

In the initial FINA decision, released in January 2019, the governing body agreed that Sun's refusal to cooperate with testers from IDTM, a FINA-hired agency, was reasonable based on an independent FINA panel's ruling that the three IDTM employees failed to show adequate proof of identification and authorization, as Sun claimed. The incident involved the destruction of a blood sample, which was witnessed by his entourage and the testers.

WADA later decided to seek the suspension against Sun and appealed the FINA ruling in March to the arbitration court. The court held a public hearing on the case on Nov 15 in Montreux, Switzerland. In a statement released on Friday, the Chinese Swimming Association voiced strong support for Sun's decision to appeal the ban while urging relevant doping control authorities to improve their protocols for the benefit of athletes.

Due to "hiring unprofessional and ineligible employees to conduct samples during testing, the doping control procedure was illegal and invalid", CSA said in the statement.

"We fully support Sun in safeguarding his legal rights. In the meantime, we hope WADA, each sport's governing body and all doping-control agencies improve their respective protocols while strictly following the rules of personnel qualification and certification."

According to the court of arbitration's website, an appeal is "allowed on a very limited number of grounds", such as lack of jurisdiction or violation of elementary procedural rules, within a time limit of 30 days.

According to a CAS statement, the court upheld the WADA appeal after concluding that the testimony by Sun and his legal team in support of his refusal was not compelling enough.

"The CAS panel found that the personnel in charge of the doping control complied with all applicable requirements as set out in the International

Standard for Testing and Investigation," the statement said.

The CAS statement also said Sun's athletic achievements before the verdict would not be nullified.

The 29-year-old Sun has won three Olympic gold medals.