Alexander Zverev did not consult tournament doctors before taking to the court for his defeat by teenager Jannik Sinner at the French Open while feeling unwell.
The US Open finalist called for the doctor early on in the match and admitted after his 6-3 6-3 4-6 6-3 loss to 19-year-old Sinner that he had been suffering from a fever.
Players are tested regularly for Covid-19 but tournaments organisers revealed on Sunday evening that Zverev's last test was on September 29 and that he had not sought advice before playing.
The statement read: "Zverev is up to date on his tests, which have all been negative. His last test was on September 29, with results received on September 30.
"Today he received a reminder for his next test, to be carried out within five days of the previous results. He did not consult the tournament doctors before his match."
Zverev kept his face mask on during his press conference, and said: "I'm completely sick. I can't really breathe, as you can hear by my voice. I had a fever as well. I shouldn't have played."
The fifth seed was criticised for going to a party after saying he would isolate following the disastrous Adria Tour this summer.
Whatever Zverev's health, this was nevertheless a very impressive performance from Sinner, who has been strangely under the radar this week despite being the hottest teenage prospect in men's tennis.
He showed in winning the Next Gen ATP Finals last year that his explosive game and fearlessness make him a hugely exciting talent, and it has not taken him long to produce that on a grand slam stage.
This is the Italian's debut at Roland Garros and he will get the chance to test himself against Rafael Nadal after coming through a series of close games in the fourth set.
His celebrations have been understated throughout the tournament, and he said: "It's great to reach the quarter-finals here. I am quite calm, so even if inside I'm very happy and I don't show that so much.
"But there is still a lot of work to do. Physically, technically, everything. It's a long way. I'm very happy that I have reached the quarter-finals."
Sinner is the first debutant to make it this far at Roland Garros since Nadal won his first title in 2005, and the youngest man to reach the quarter-finals at a slam since Novak Djokovic 14 years ago.
Sinner may not want to watch a replay of Nadal's performance against another up-and-coming young player, Sebastian Korda, in the fourth round.
Korda, 20, idolised Nadal to such an extent that he named his cat after him but the Spaniard was in a ruthless mood and allowed the American just four games in a 6-1 6-1 6-2 victory.
Nadal grew up watching Korda's father Petr, a former Australian Open champion, who said his son would experience playing in Nadal's living room.
It certainly felt like that, with Korda's only real chance coming at the start of the third set, when he led 2-0, only for Nadal to reel off six games in a row.
The scoreline certainly did not ruin the occasion for Korda, though, who was able to appreciate Nadal's shots even as they were flying past him and used the opportunity to ask his hero for an autograph.
Korda said: "Ever since I was a kid, I was in love with him and everything about him. I would watch every single match.
"He almost hit an around-the-net forehand and I was kind of begging for it to go in because that would have been the coolest thing ever.
"And then he hit a running forehand winner on me at the lines. I just said to myself, 'This is awesome'.
"I don't know if anyone's ever asked him for an autograph after a match, but that was definitely the coolest moment of my life and one I'll never forget for sure."
Nadal has lost just 23 games in four matches, and the concerns about the conditions making life tough for him seem a long time ago.
The second seed said: "I'm in the quarter-finals without losing a set and having very positive scores.
"So I can't complain at all. I am quite happy about the way that I am playing and the practices I am feeling every time a little bit better and better."
