Nick Kyrgios faces further punishment after being booed off court

After his incendiary remark towards Wawrinka was detected by a courtside microphone during their second-round match on Wednesday, Kyrgios took to Twitter and Facebook to apologise for the incident but it did not stop the Association of Tennis Professionals (ATP) from taking quick action.

"Nick Kyrgios has been fined the maximum on site amount of $10,000 for an insulting comment he made to Stan Wawrinka," an ATP spokesperson said in a statement on Thursday.

"The ATP...is still reviewing that matter and additional penalties may be forthcoming."

The other shoe dropped a few hours later when the ATP issued another statement that an additional fine of $2,500 had been imposed for "Unsportsmanlike Conduct related to a comment made to a ball person during the match."

Kyrgios entered his last-16 match to boos and exited the same way after falling 7-5 6-3 to big-hitting American John Isner.

The Australian had insulted Swiss opponent Stan Wawrinka on Wednesday during their second round encounter.

Prior to the match the ATP had fined Kyrgios $10,000, the maximum penalty available, for remarks directed at Wawrinka about his girlfriend picked up by a courtside microphone.

With Isner serving for the match there were more boos for Kyrgios who lost his cool again engaging in a heated exchange with a spectator yelling "You're so tough man, so tough".

More significantly, the ATP raised the possibility that Kyrgios could be suspended.

"Kyrgios has been served with a 'Notice of Investigation' which begins a process to determine if his actions also constitute a violation of the Player Major Offence provisions set forth under 'Aggravated Behavior' or 'Conduct Contrary to the Integrity of the Game'.

"That investigation opens up the possibility of further penalties which could include additional monetary fines and/or suspension from ATP events."

A couple of hours after the ATP announced it would fine Kyrgios, the 20-year-old player went into damage control mode.

"I would like to take this opportunity to apologise for the comments I made during the match last night vs Stan," Kyrgios tweeted.

He also posted the comment on Facebook, adding: "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."

Kyrgios, in the comment picked up by a courtside microphone, said to Wawrinka: "Kokkinakis banged your girlfriend," referring to his Davis Cup team mate Thanasi Kokkinakis. "Sorry to tell you that, mate."

French Open champion Wawrinka, who separated from his wife last year, has been linked with Croatian WTA Tour player Donna Vekic, as has Kokkinakis.

Wawrinka did not appear to hear the comment at the time, but he was furious afterwards, calling at his official press conference and via Twitter for the ATP to take disciplinary action against Kyrgios.

"What was said I wouldn't say to my worst enemy. To stop so low is not only unacceptable but also beyond belief," he tweeted.

Kyrgios said after he had won the match 6-7(8) 6-3 4-0, following Wawrinka's retirement due to a back injury, that he had been responding to words from the two-time grand slam champion.

"He was getting a bit lippy with me," Kyrgios said of Wawrinka. "Kind of in the heat of the moment. I don't know. I just said it."

Kyrgios, who was beaten in the third round by American John Isner on Thursday, told reporters after the loss that as far as he was concerned the case was closed.

He spoke before the ATP announced that it was not.