Stefanos Tsitsipas accused a chair umpire of being biased against him and called the official a "weirdo" during a rant in a first-round exit at the US Open.
Tsitsipas told Damien Dumusois that the cause of his bias was "because you're French probably and you're all weirdos!", as he suffered a second consecutive first-round exit at a Grand Slam.
The argument came midway through the fourth set of Tsitsipas' 6-4 6-7 (5-7) 7-6 (9-7) 7-5 defeat to Andrey Rublev, when the eighth seed from Greece appeared to be battling cramps and was slow to return to the court after losing his serve.
Dumusois told Tsitsipas it was time to play, but Tsitsipas was still reaching into his bag for a new headband and screamed at Dumusois that he still needed time to change.
When told by Dumusois that he would be penalised, Tsitsipas replied: "I don't care. Do whatever you want, because you're the worst."
"I don't know what you have against me," Tsitsipas continued. "Because you're French probably and you're all weirdos! You're all weirdos!"
Tsitsipas had been angry that Dumusois believed he was getting coaching during the match from his father, Apostolos, which is not allowed.
"The chair umpire was very incorrect in what he was telling me during the match," Tsitsipas said after the defeat against Rublev, who beat Roger Federer at Cincinnati.
"I don't know what this chair umpire has in specific against my team, but he's been complaining and telling me that my team talks all of the time when I'm out on the court playing.
"I believe he's not right, because I never hear anything of what my team says from the outside."
Tsitsipas added that he thought tennis needed more umpires who are fair to all players.
"I feel like some of them have preferences when they are on the court," he said.
Elsewhere, fourth seed Dominic Thiem was also knocked out in four sets by Italian Thomas Fabbiano, ranked world No 87.
The Austrian, who also lost in the first round at Wimbledon, has been struggling with a virus in the build-up to the US Open and was beaten 6-4 3-6 6-3 6-2.
However, Alexander Zverev survived an upset as the sixth seed defeated Radu Albot of Moldova in five sets.
The German eased into a two sets to love lead, before he was pushed the distance as he progressed 6-1 6-3 3-6 4-6 6-2.