Nick Kyrgios has been caught on camera groping his girlfriend Costeen Hatzi at the Australian Open.

In a behind-the-scenes video posted to Twitter, Kyrgios and Hatzi are seen walking around in the players warm-up area at Melbourne Park.

The tennis star, 27, then walks behind his girlfriend and wraps his arms around her before groping her chest.

Stunned viewers flocked to social media to react to the video, with one person writing: 'No comment.'

'Why is he doing that in the middle of the hallway why is he even at the tournament?' another said.

'Like the most annoying couple in a high school hallway. Also get outta here. Why is he still here?' a third wrote.

It comes after the tennis bad boy withdrew from the Australian Open and announced he'd be returning to his mother's home for knee surgery in the coming fortnight. 

The shock decision came just a day before he was due to play his first-round match against Roman Safiullin in the latest hammer blow to the tournament.

He was Australia's best chance of taking out a title at the grand slam and was originally battling an ankle injury that prevented him from competing in any of the warm-up tournaments before play started at Melbourne Park.

A routine MRI, which was done after Nick suffered discomfort in his knee, revealed he has a tear in his lateral meniscus and a cyst, his physiotherapist Will Maher explained.

He said the injury isn't serious enough to be career-threatening and it only became a problem in the last two weeks.

The star said he was shattered to have to withdraw from his home grand slam, where many rated him a chance of going one better than he did at Wimbledon, where he lost the final to Novak Djokovic last year.