Tennis superstar Nick Kyrgios and his girlfriend Costeen Hatzi were spotted looking glum as they arrived back in Sydney on Thursday afternoon.

The sighting comes just days after the Australian tennis player announced his withdrawal from the Australian Open due to a knee injury.

The 27-year-old, who has been dating Hatzi since 2021, was seen walking through Sydney airport with his head down, looking visibly upset.

The Australian tennis star was seen wearing a white Lakers sweater, which he teamed up with a pair of basketball shorts and a pair of red and white sneakers.

Costeen also got the sweater memo, teaming hers with a pair of black leggings and sneakers.

Kyrgios, who had been widely tipped to go deep into the tournament, was forced to pull out of the Australian Open on Monday after scans revealed a cyst on a small tear in the meniscus of his left knee.

'I'm devastated obviously,' Kyrgios said in a statement.

'It's my home tournament. I've had some great memories here. Obviously, last year winning the title in doubles and playing the best tennis of my life probably.'

'Then going into this event as one of the favourites, it's brutal. All I can do now is just look forward, do what I need to do and come back.'

Kyrgios' physiotherapist Will Maher revealed a small tear in the Australian's left meniscus had caused a cyst to develop, which will need to be removed surgically.

Costeen Hatzi, a Sydney-based style blogger, has been Kyrgios' biggest supporter throughout his career.

She was by his side as he announced his withdrawal from the tournament and has been by his side ever since.

Kyrgios has made a name for himself as one of the best young talents on the tour and his withdrawal from the Australian Open is a big blow for the sport.

Kyrgios is expected to return to the court once he has fully recovered from his injury. He is yet to make an announcement on his return date.