Nick Kyrgios has refused to back down in his war of words with Stefanos Tsitsipas' mother, posting a thinly veiled dig on Instagram.

Kyrgios and Tsitsipas were involved in a volatile clash at Wimbledon earlier this year, with the Australian's antics not sitting well with his Greek rival, who crashed out after a four-set thriller.

Tsitsipas' mother, Julia Apostoli, claimed that the reason her son lost that match was because he refused to stoop to Kyrgios' level and play 'dirty tennis'.

'Our match turned out to be very nervous with Nick Kyrgios,' she said

'That is, we were practically offered to play dirty tennis there, but we don't know how to play such tennis. Therefore, Styopa [her nickname for Stefanos] lost his temper and left the court without getting there.' 

But now, Kyrgios has mocked those comments on Instagram. Sharing a video clip from that match in England, he posted the caption: 'Dirty tennis'.  

Kyrgios and Tsitsipas' relationship has been frosty over the years. The pair first exchanged words on social media in 2018 but appeared to bury the hatchet a year later when they teamed up as doubles partners at the Washington Open.

But things have since soured with Tsitsipas accusing the Australian of being a 'bully' and 'evil' in the immediate aftermath of his fourth round loss.

Kyrgios responded: 'I just think he's making that match about me, like he's got some serious issues, like serious.' He also added that Tsitsipas was 'not liked' in the locker room.