World No. 3 Dominic Thiem is “extremely sorry” for the way players conducted themselves at Novak Djokovic’s Adria Tour exhibition event after which four participants tested positive for the novel coronavirus, the Austrian said on Thursday.

Djokovic, Grigor Dimitrov, Borna Coric and Viktor Troicki tested positive after playing in the charity tournament in Serbia and Croatia.

Australian Open finalist Thiem played in and won the Belgrade leg, which was staged at Djokovic’s tennis centre by the Danube River.

The 26-year-old, who lost to Djokovic in the Melbourne final, said he was “shocked” when he got the news from the Adria Tour. Thiem has tested negative for the virus.

“We played without an audience for weeks, so we have been more than happy about the fans at the event,” Thiem said in an Instagram post. “We trusted the Serbian government’s corona rules, but we have been too optimistic.

“Our behaviour was a mistake, we acted too euphorically. I am extremely sorry.”