Nick Kyrgios says it was a "bone-headed decision" to go ahead with the Adria Tour after Grigor Dimitrov and Borna Coric tested positive for coronavirus.
Bulgarian world number 19 Dimitrov, 29, withdrew from the tournament in Zadar, Croatia, on Saturday with sickness after losing to 23-year-old Croatian Coric, who played again on Sunday.
The series of events is hosted by world number one Novak Djokovic.
"Boneheaded decision to go ahead with the 'exhibition'," Kyrgios said.
With Croatia easing lockdown measures before the event, players were not obliged to observe social distancing rules and were seen embracing at the net at the end of their matches.