Nick Kyrgios fined for insulting remark about Stan Wawrinka's girlfriend

The ATP has fined Nick Kyrgios for his "insulting remark" towards triple major champion Stan Wawrinka during a match at the Montreal Masters.

The ATP said that Kyrgios had been fined the maximum on-site amount of $10,000 but added that they were "reviewing the matter and additional penalties may be forthcoming".

Kyrgios says he is sorry for his behaviour, writing on Facebook: "I would like to take this opportunity to apologise for the comments I made during the match last night vs Stan Wawrinka.

"My comments were made in the heat of the moment and were unacceptable on many levels. In addition to the private apology I’ve made, I would like to make a public apology as well.

"I take full responsibility for my actions and regret what happened."

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Wawrinka had urged tennis authorities to take action in a post on social media earlier on Thursday.

On Wednesday night, a courtside microphone picked up Kyrgios making an insulting remark about Croatian player Donna Vekic, who is reportedly Wawrinka's girlfriend.

Wawrinka later tweeted: "There is no need for this kind of behaviour on or off the court and I hope the governing body of this sport does not stand for this."

Kyrgios beat Wawrinka 6-7 (6-8), 6-3, 4-0 when the 2015 Australian and French Open champion retired hurt with a back injury.