Tennis bad boy Nick Kyrgios has been criticised for trash-talking opponent Stanislas Wawrinka during a match in Montreal on Thursday (AEST).

Kyrgios, no stranger to controversy in his short but incident-filled career, moved into the third round of the Rogers Cup event after the Swiss player retired with an injury in the third set of their clash.

VIDEO: Watch Kyrgios’ incredible Wawrinka sledge

The 20-year-old Australian led 4-0 in the last set before Wawrinka pulled the pin but it was not his victory over the world number five that will dominate tennis discussion in the next few days.

Instead, it will focus on Kyrgios’ comment to Wawrinka, which referred to fellow Australian youngster Thanasi Kokkinakis and was picked up by television cameras.

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Kyrgios told his opponent: “Kokkinakis banged your girlfriend, sorry to tell you that.”

Wawrinka’s coach, former professional Magnus Norman of Sweden, got stuck into Kyrgios on Twitter.

“That was really really low Nick Kyrgios,” he posted.

“Hope for u [sic] that u have people around that will teach u a thing or 2 about life tonight. Very bad.”

Victoria Azarenka, world number 21 on the women’s circuit, also criticised Kyrgios on the social media platform.

“At least walk away from the microphone,” Azarenka wrote.

“U have to respect ur opponent… Everyone has to… Always.”