Nick Kyrgios has apologised after courtside microphones caught him sledging Stan Wawrinka, and says the comments were made in “the heat of the moment”.

The Australian has been fined by the ATP for his comments to Wawrinka during the second-round Rogers Cup match in Montreal on Wednesday.

Kyrgios, 20, linked the reigning Australian and French Open champion with teenage Australian player, Thanasi Kokkinakis.

“Kokkinakis banged your girlfriend. Sorry to tell you that mate,” said Kyrgios midway through the second set.

Two-time grand slam winner Wawrinka divorced his wife Ilham earlier this year and has since been romantically linked with Croatian teenager Donna Vekic.

The world No.5 appeared to not hear the comment at the time, but unleashed after the match, won by Kyrgios 6-7 (8-10) 6-3 4-0 after Wawrinka retired with a back injury.

“He’s young but that’s no excuse … every match, he behaves very badly,” Wawrinka told reporters in French.

“The problem is he doesn’t just behave badly towards himself, he behaves badly towards the people around, the other players, the ball kids, the umpires.

“I really hope the ATP will take major action against him this time.”

Wawrinka’s call was answered by the tennis association, which announced on Thursday that it was fining Kyrgios for the comments. It did not give details of an amount.

Shortly after the release of the ATP statement, Kyrgios made a public apology on Facebook and Twitter.

“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.”