John McEnroe has praised Jannik Sinner’s “mental resilience” after the world No.1 reached the US Open semi-finals following his controversial drug case.

And the American legend admitted it would be “super depressing for our sport” if the Italian were to be guilty of doping.

Sinner twice tested positive for a banned substance in March but escaped a ban on the eve of the US Open after the International Tennis Integrity Agency accepted that the Italian star had been accidentally contaminated during a massage.

The speed of the “no fault” verdict enraged some players with Nick Kyrgios claiming it was “ridiculous” there was no ban. The Italian, who won his final warm-up event at the Cincinnati Masters, has been the talk of the final Grand Slam of the season.

But after Australian Open champion Sinner set up a semi-final clash with British No.1 Jack Draper, McEnroe told ESPN: “I give him a lot of credit for the mental resilience he has shown over the last few weeks. In the first round, he lost the first set and he was down a break. You were like: ‘What’s going on?’ Stuff’s swirling in his head. So a lot of kudos for Jannik Sinner and the way he has played.

“Would there be a stain or an asterisk if he were to win a second Major here? My opinion would be no. I wish this had been decided quicker, the whole episode when it came out. I sure hope there was nothing to it. It would be absolutely super depressing for our sport. He is one of our brightest young stars.”

Sinner has now reached the semi-final or better in all four Majors and the Australian Open winner is bidding to win both hardcourt Slams this season.

After beating 2021 champion Daniil Medvedev in four sets in the quarter-finals, the Italian was asked how he had been able to keep focused on his day job.

“I have my team and my people who are close to me,” he said. “They know me, they know I always stick with the people who know me and believe me.

It's a very important part. And obviously, I'm very happy to have them, you know, coach-wise and also off the court.

“Yeah, obviously in the beginning it was a tough situation, but, day by day it has got better. So yeah, I'm happy about that. Let's see now in the semis what I can do.”

Novak Djokovic called for "clear protocols" and "standardised approaches" to doping cases while Roger Federer stated: "It’s not something we want to see in our sport, these types of news, regardless if he did something or not, or any player did. It’s just noise that we don’t want."

But his semi-final opponent Draper has supported his friend - and said he had sympathy with the social media storm following his controversial match point against Felix Auger Aliassime in Cincinnati last month.

Speaking before the US Open, the British No.1 said: “I thought my situation was tough to deal with. He must be going through a lot right now. Obviously I am quite close with Jannik and I'd honestly say that he's, in terms of players, he's one of the nicest, most genuine, kind, professional guys that I've been around on the tour.

I really don't think he would have had any idea of any of what's gone on with him. All I know is that I really don't think Jannik would have had any clue about what was going on. “And for him to know about this, what's been going on, and know about these things, and carry that on his shoulders for the last, four or five months, and make semis of Grand Slams and win Masters events. I think his mental strength is, you know, I don't think many people could have done that.”