One of three anti-doping officials in the Sun Yang anti-doping saga says he knows nothing about anti-doping and is just a builder helping out an old classmate after they ran into each other at a school reunion.

Key points: The man gave his version of events under the condition of anonymity

The man gave his version of events under the condition of anonymity He said he had not been trained to conduct doping tests, adding "it is unnecessary for me to undertake such training"

He said he had not been trained to conduct doping tests, adding "it is unnecessary for me to undertake such training" The Court of Arbitration for Sport is expected to deliver its decision on Sun Yang's case in the new year

The news comes just days after a marathon Court of Arbitration for Sport (CAS) hearing where the World Anti-Doping Agency (WADA) was seeking a ban against the Chinese swimmer for failing to comply with a sample collection last year.

Last September, a doping control team arrived at Sun's home in Zhejiang province for an out-of-competition blood and urine test.

Sun allowed his blood to be taken, but then refused to provide a urine sample after questioning the testers' credentials.

The evening ended in a stand-off with Sun's doctor refusing to let the blood vials be taken while the testers refused to leave without their container.

A security guard from the compound where the swimmer lives used a hammer to break open the container.

A FINA tribunal originally found in the swimmer's favour but WADA has appealed that decision.

In an 11-hour hearing numerous witnesses were called, although none of the three-member doping control party from the night in question appeared in person for the televised hearing.

In a one-on-one interview with China's Xinhua News Agency, the unnamed anti-doping official agreed to give his version of events but asked for anonymity.

"I knew nothing about the doping test and nothing about my role that night. I just came to help my middle school classmate at her request. I am a builder," the man said.

He went on to say he had given his statement in written form to the Court of Arbitration for Sport and WADA in the days before the hearing but did not appear in person.

"I am a builder and I am always busy at work, day and night," he said.

"No-one ever trained me about the doping test, and it is unnecessary for me to undertake such training."

This is at odds with the testimony given by an International Doping Tests and Management (IDTM) official called as a WADA witness at the CAS hearing.

Tudo Popa was the IDTM program manager tasked with coordinating the test team from his office in Stockholm.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 24 seconds 24 s Britain's Duncan Scott refuses to shake hands with China's Sun Yang

When asked whether all three members of the testing party were "trained and authorised" to perform their duties on the night he replied "Yes".

Mr Popa was also asked about the doping control assistant (DCA) [the construction worker] specifically.

"His role was strictly to witness the passing of the sample from the athlete's body to the collection vessel," Mr Popa said.

He said IDTM had a signed document from the DCA that confirms he was trained and informed about his "rights and responsibilities" including the need for confidentiality.

During the test Sun became suspicious when the man started taking photos, which is against anti-doping protocols.

"Sun is a big star in China and it was my first time being near him. I was excited. I took a couple of pictures outside the room with my [mobile phone]," the DCA said.

The CAS tribunal is expected to reach and deliver a decision in the new year. ( Reuters: Antonio Bronic )

"When I tried to take pictures of him again when we were sitting in the room, Sun told me not to do so.

"Then he asked every one of us to identify ourselves. I showed my ID card. Sun pointed out that I was not an accredited tester and should not stay in the test room."

Xinhua said while the man waited outside, the woman in charge of the testers came out numerous times to show him a document on her iPad.

"I did not know English and did not understand what she was talking about. Then I gave the iPad back to her. I didn't know what happened in the test room," the DCA said.

The CAS tribunal is expected to deliver its decision in the new year.