Sun Yang is claimed to have breached the terms of his doping ban ©Getty Images

Banned Chinese swimmer Sun Yang could face further punishment after seemingly training at an official high-performance facility, which would be in breach of his current anti-doping sanction.

The three-time Olympic champion was banned for four years and three months earlier this year at the conclusion of a long-running legal saga.

Yet Sun, whose period of eligibility is set to end on May 28 2024, shortly before the Paris 2024 Olympics, was seen on social media training at a restricted facility, according to The Times.

The World Anti-Doping Agency (WADA) has said it will investigate.

"We are looking into the matter and, as part of that, we will follow up with the relevant entities, including the International Swimming Federation (FINA), to gather more information and to be in a position to determine whether the swimmer has breached the terms of his suspension, as per the decision of the Court of Arbitration for Sport of 22 June 2021," read a WADA statement.

FINA confirmed it was "contacting the Chinese authorities to seek explanation and will reiterate that it is imperative that any banned athlete complies with the WADA Code and the conditions of their ineligibility", according to The Times.

Sun's current ban stems from a September 2018 drugs test, where a member of his entourage smashed a blood vial with a hammer.

FINA let Sun off with a warning, but WADA appealed to the CAS.

Sun Yang requested an in-person Court of Arbitration for Sport hearing the first time around ©Getty Images
Sun Yang requested an in-person Court of Arbitration for Sport hearing the first time around ©Getty Images

Sun had already served a three-month ban in 2014 after testing positive for trimetazidine.

The swimmer claimed his doctor prescribed it for his heart palpitations and WADA did not pursue that case further after an investigation.

For the second offence, after an in-person CAS hearing, Sun was banned for eight years in February 2020 - only for that sanction to be squashed on appeal to the Swiss Federal Tribunal.

The sanction was thrown out after racist tweets from CAS panel President Franco Frattini, a former Italian Foreign Minister, came to light, and another hearing was ordered.

The verdict of the second CAS hearing was Sun being banned for four years and three months.

That sanction was backed to begin on February 28 2020, making the 11-time World Championships gold medalist eligible to return shortly before the Paris 2024 Olympics.

Any additional period of eligibility would likely rule Sun out of Paris 2024.

Sun will be 32 by the time of the next Summer Olympic Games.