Defending US Open champion Novak Djokovic has attacked tennis’s anti-doping programme for a “lack of consistency” in the wake of last week’s revelations about world No1 Jannik Sinner.

Djokovic also called for changes to the rules, which allowed Sinner to play on without disclosure after two urine tests – both carried out in March – picked up traces of the banned steroid clostebol.

News of the positive tests was finally released last week, along with the “no fault or negligence” verdict from the International Tennis Integrity Agency, which ruled that Sinner had suffered unwitting contamination via a sports massage administered by his physical trainer.

Nick Kyrgios, Denis Shapovalov and Britain’s Liam Broady were among the players who publicly queried how Sinner had got off so lightly, and Djokovic said on Friday that he could see their point.

“I understand the frustration of the players is there because of lack of consistency,” Djokovic told reporters in New York, where he is due to begin his quest for a 25th major title on Monday.

“As I understood, his case was cleared the moment basically it was announced. But, you know, I think five or six months passed since the news was brought to him [Sinner] and his team.

“So, yeah, there is a lot of issues in the system. We see lack of standardised and clear protocols. I can understand the sentiments of a lot of players that are questioning whether they are treated the same.

“Hopefully the governing bodies of our sport will be able to learn from this case and have a better approach for the future. I think collectively there has to be a change, and I think that’s obvious.

“Many players – without naming any of them – I’m sure you know already who these players are, have had similar or same, pretty much the same cases, where they haven’t had the same outcome, and now the question is whether it is a case of the funds, whether a player can afford to pay a significant amount of money for a law firm that would then more efficiently represent his or her case.”

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Former world No1 Simona Halep and British doubles specialist Tara Moore are among the players who spent many months serving suspensions for doping offences, only for their names to eventually be cleared.

There has been a high incidence of clostebol cases in Italy in recent years, with 38 Italian athletes testing positive between 2019 and 2023. This is one of the few countries where clostebol is available in over-the-counter products.

In Sinner’s case, his lawyers argued that the source of the contamination was a widely available healing spray used by his physio, Giacomo Naldi, after Naldi had cut his finger on a scalpel in his treatment bag.

On Friday, Sinner revealed that he had dismissed both Naldi and Umberto Ferrara – the fitness coach who had supplied the steroid – from his team.

“Now, because of these mistakes, I’m not feeling that confident to continue with them,” said Sinner, who is 23. “The only thing I just need right now, just some clean air.”