Tomic played against Russian rising star Roman Safiullin on Tuesday and made a quick exit after he lost 6-1, 6-4.
Tomic told umpire Aline Da Rocha Nocinto at the change-over that he thought he was infected.
He said "I'm sure in the next two days I will test positive, I'm telling you," the 29-year-old said from his chair.
"I'll buy you dinner if I don't test positive in three days, otherwise you buy me dinner."
Tomic revealed that he could not believe that there was no PCR testing for players.
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Tomic has not played in an ATP tournament since September when he failed to qualify in an event in Kazakhstan.