Outspoken Australian Nick Kyrgios questioned Dominic Thiem's intellect Wednesday after the world number three told him to stop criticising fellow tennis stars Alexander Zverev and Novak Djokovic for taking risks with the coronavirus.

Kyrgios said Thiem wasn't on the same "intellectual level" after the Austrian called his criticism "cheap" and claimed it was "bad luck" that Zverev was caught partying after promising to self-isolate. Djokovic, Grigor Dimitrov, Borna Coric and Viktor Troicki all tested positive for COVID-19 after last month's Adria Tour, an exhibition series with minimal social distancing where Thiem and Zverev also played.

"Kyrgios has really done a lot of nonsense himself. That's why I understand even less when he interferes everywhere," Thiem told German media this week. "It would be better for him to come clean instead of always criticising others."

The Australian shot back on Twitter. "What are you talking about @ThiemDomi? Mistakes like smashing rackets? Swearing? Tanking a few matches here or there? Which everyone does? None of you have the intellectual level to even understand where I'm coming from. I'm trying to hold them accountable."

Kyrgios added: "This just shows what a joke @ThiemDomi @AlexZverev & @DjokerNole think this is, 2 of them partying like potato's during a global pandemic. People losing lives, loved ones and friends, and then Thiem standing up for the 'mistake'. These guys are the 'top' of our sport. SMH (shaking my head)."

Last week Kyrgios also exchanged verbal blows with German legend Boris Becker, who called him a "rat" for singling out Zverev.

"@TheBorisBecker is a bigger doughnut than I thought. Can hit a volley, obviously not the sharpest tool in the shed though," he fired back.

Zverev vowed to self-isolate after the Adria Tour, only to be filmed days later in a busy bar in footage that went viral.