Jannik Sinner is still at risk of being banned from tennis after the World Anti-Doping Agency (WADA) decided to appeal against an independent ruling that cleared the world No 1 of responsibility for testing positive for a banned substance.

Sinner first tested positive for banned anabolic steroid clostebol during Indian Wells on March 10, then again eight days later.

He was provisionally suspended, but on both occasions he successfully appealed and was allowed to continue playing while the evidence was assessed.

The International Tennis Integrity Agency took the case to an independent tribunal in August, when Sinner’s explanation for why there had been an extremely small quantity of clostebol in his system – less than a billionth of a gram – was accepted.

Sinner was successful in convincing the tribunal that his two positive tests had been a consequence of contamination.

The explanation provided by Sinner was that a month before travelling to Indian Wells, fitness coach Umberto Ferrara bought an over-the-counter spray containing clostebol in Italy. Then during the Indian Wells event, physio Giacomo Naldi cut his finger and was advised by Ferrara to use the spray to treat the wound.

According to a statement from the Sinner team: ‘The physiotherapist treated Jannik and his lack of care coupled with various open wounds on Jannik’s body caused the contamination.’

The tribunal heard that Sinner suffers from skin condition psoriasiform dermatitis, which can cause irritation and, if scratched, cuts and sores. This was accepted as the reason for the clostebol entering his body via the physio’s finger.

Sinner has since dismissed both Ferrara and Naldi from his team.

On September 26, the World Anti-Doping Agency appealed against the verdict that there was ‘no fault or negligence’ on Sinner’s behalf.

WADA argues that the ruling is not in line with the applicable rules.

The International Tennis Integrity Agency has acknowledged WADA’s right to take the case to the Court of Arbitration for Sport (CAS).

There is no date set for Sinner’s case to be heard by CAS as things stand.

It is possible that the hearing may not take place until next year.

Sinner remains eligible to play in all tournaments but that could change if CAS decides to overrule the previous ruling.

WADA has suggested it would like to see Sinner ruled ineligible for a period of between one and two years.

However, WADA do not want to see Sinner disqualified from any events he has already taken part in. For example, they do not want to see him stripped of the US Open singles title he won in New York on September 8.