The Russian was trailing 6:5 in the third set against Alexander Boublek, when he appeared to say something to the line judge.

An ATP supervisor came down to the court, accompanied by a Russian speaker who claimed that Rublev had sworn in his native language.

Rublev protested, insisted he'd been speaking in English, while Boublek also backed his opponent.

But the 26-year-old was defaulted by umpire Miriam Blay, and made jeers from the crowd in Dubai.