Jannik Sinner is facing the renewed threat of a ban after the World Anti-Doping Agency (Wada) launched an appeal against a ruling of “no fault or negligence” for two positive tests the world No 1 returned in March.

Sinner, who won the US Open this month, twice tested positive for an anabolic steroid in March, but on 20 August the International Tennis Integrity Agency (ITIA) determined he was not to blame and imposed no punishment.

The ITIA 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 (Cas), seeking to impose a ban of up to two years on the 23-year-old Italian.

A statement from the agency read: “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.”

The ITIA said in a statement on Saturday: “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.“

Sinner said his physio, Giacomo Naldi, applied an over-the-counter spray containing clostebol to his skin to treat a small finger wound and then administered massages between 5 and 13 March without using gloves, according to the ITIA.

Italy’s Sinner has maintained his innocence, saying the amount of clostebol found in his system was less than a billionth of a gram. However, some players criticised the verdict, saying Sinner’s explanation “made no sense”.

Sinner’s representatives did not immediately respond to a request for comment on Wada’s appeal. He is in Beijing defending his China Open title, where he beat Roman Safiullin 3-6, 6-2, 6-3 to reach the quarter-finals on Saturday.