(CNN)Nick Kyrgios was fined $10,000 by the ATP after sledging Stan Wawrinka at the Rogers Cup in Montreal and more action may yet be taken against the controversial Australian.
Microphones courtside picked up Kyrgios' lewd comment -- he linked the Swiss' apparent girlfriend to men's pro Thanasi Kokkinakis -- on Wednesday although the two-time grand slam champion didn't appear to hear it at the time.
Such behavior might be commonplace in other sports but is extremely rare in tennis.
The ATP earlier Thursday said that the 20-year-old had been fined for what it called an "insulting remark" during the second round contest and disclosed the amount several hours later, after Kyrgios was notified. The $10,000 sum is the maximum financial penalty allowed on site, according to the ATP.
The men's governing body, though, "is still reviewing" the incident "and additional penalties may be forthcoming," an ATP spokesman said in an email sent to CNN.com.
It's not the first time Kyrgios has been sanctioned financially: He was forced to relinquish $9,500 at Wimbledon for unsportsmanlike conduct and uttering an audible obscenity.
Kyrgios, who has pocketed about $790,000 in prize money in 2015, issued an apology on his Facebook page.
"I would like to take this opportunity to apologize for the comments I made during the match last night vs Stan Wawrinka," said Kyrgios. "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."
A livid Wawrinka -- who divorced wife Ilham earlier this year -- had called on the ATP to penalize the world No. 41 and said he confronted Kyrgios in the locker room.
"It's not the first time that he has big problems on the court in terms of what he says and in terms of how he acts," Wawrinka, who retired in the third set with a back injury, told reporters in French in a video that was posted online and translated by tennis blogger Stephanie Myles.
"I just hope