The fall-out from Jannik Sinner’s two failed drug tests at the Indian Wells Masters tournament in March continues, with tennis legend John McEnroe admitting he is stunned by the story.

It was revealed on Tuesday that Sinner failed two anti-doping tests in March but has been absolved of fault or negligence by the International Tennis Integrity Agency (ITIA).

The ITIA accepted Sinner’s explanation that the banned substance clostebol, an anabolic agent that can aid muscle growth, had accidentally entered his system via a product one of his team had used to treat a small wound.

Sinner was first told of his doping violation in April and, while he has won tournaments in Halle and Cincinnati, the Italian pulled out of the Paris Games after a bout of tonsillitis and his coach Darren Cahill feels the investigation had started to wear down the 23-year-old.

Cahill told ESPN: “I guess if you are not a Jannik fan, you may not see too much difference in what he has been doing the last few months because he has still been playing quite well.

“But if you are a Jannik fan, you would have seen a big change in his body language, physicality on the court, his excitement to be on the court – he’s struggled and I think it’s worn him down physically and mentally.

“He got tonsillitis, which is the reason why he missed the Olympics.

“I just want to stress that he’s maybe the most professional young man that I have ever had the chance to work with. He would never ever intentionally do anything and he’s in a situation that is incredibly unfortunate.”

Sinner first tested positive on March 10 while competing in Indian Wells and was red-flagged again in an out-of-competition test eight days later.

Both samples yielded trace amounts of clostebol but he was able to continue playing on the ATP Tour after successfully challenging a provisional suspension.

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Scientific experts consulted by the ITIA concluded Sinner’s account – in which his physiotherapist had used an over-the-counter spray containing clostebol on his skin between March 5 to 13 – was credible.

Speaking at a Eurosport event ahead of the US Open, seven-time Grand Slam champion McEnroe joined the tennis world in expressing his shock at the news, with one strand of the debate since the news was made public focusing on how the case was handled by tennis chiefs.

Most players are suspended when they fail two drug tests, but Sinner was allowed to continue and his story was kept quiet until he was cleared on Tuesday, which was a very different scenario to that endured by former world No 1 Simona Halep.

She was banned from the sport while she appealed against her ban, with McEnroe suggesting there are still some holes to be filled in this story.

“First of all, I think it takes too long for these things to be resolved,” began McEnroe, speaking at a Eurosport event ahead of their US Open coverage.

“This happened in March and we are now in August. So it seems like it takes too long for everyone to find out.

“In Simona’s case, I don’t know what they found in her system and what they found in Jannik’s, but could easily see why she is upset, there is no question about that.

“Her story seemed to drag on for a couple of years and very much affected her career.

“It seems here (with Sinner) that at the moment, there’s going to be no suspension at all.

“I’m still trying to figure out what has happened. I’m not a doctor. They say there was a minute amount of whatever it was in his system. I don’t know at what point that means there is a lot of it, but let’s just say it’s unfortunate for all concerned.

“This has come out of the blue. I mean, it’s not like he looks like Hulk Hogan! It seems crazy.”

John McEnroe will be covering the US Open for Eurosport.