World number one Jannik Sinner is facing the renewed threat of a ban after the World Anti-Doping Agency launched an appeal against a ruling of “no fault or negligence” for two positive tests he returned in March.

Sinner, who won the US Open earlier this month, twice tested positive for an anabolic steroid in March but on August 20 an independent tribunal determined he was not to blame and imposed no punishment.

The tribunal accepted Sinner’s explanation that the banned substance entered his body as a result of a massage from his physio, who had used a spray containing the steroid to treat a cut on their finger.

But WADA has appealed to the Court of Arbitration for Sport, seeking to impose a ban of up to two years on the 23-year-old Italian.

A statement from the agency said: “It is WADA’s view that the finding of ‘no fault or negligence’ was not correct under the applicable rules.

“WADA is seeking a period of ineligibility of between one and two years. WADA is not seeking a disqualification of any results, save that which has already been imposed by the tribunal of first instance.”

A statement from the International Tennis Integrity Agency said: “The ITIA acknowledges the World Anti-Doping Agency (WADA) decision to appeal the ruling of no fault or negligence in the case of Italian tennis player Jannik Sinner, issued by an independent tribunal appointed by Sport Resolutions on 19 August 2024.

“Under the terms of the World Anti-Doping Code, WADA has the final right to appeal all such decisions.

“Having reached an agreed set of facts following a thorough investigative process, the case was referred to a tribunal entirely independent of the ITIA to determine level of fault and therefore sanction because of the unique set of circumstances, and lack of comparable precedent.

“The process was run according to world anti-doping code guidelines. However, the ITIA acknowledges and respects WADA’s right to appeal the independent tribunal’s decision in the Court of Arbitration for Sport.”

Sinner was on court on Saturday morning at the China Open, rallying to beat Roman Safiullin 3-6 6-2 6-3 and advance to the quarter-finals.

“A tough match. He’s an incredible player and we always have tough battles,” Sinner said. “This was our third encounter, so we know each other a bit. He returns very well, and he was serving well at important moments. So I tried to keep up mentally, which today was very tough.

“Especially on these kinds of days, when maybe you don’t feel at your 100 per cent, to find a way through means so much to me. He’s an incredible player, so I knew I had to raise my level when it counted.”