Tomic told the on-court umpire during Tuesday's qualifying session at Melbourne Park that he'll almost certainly test positive for COVID-19.
Tomic put out his trademark theatrics on Melbourne's Kia Arena on Tuesday in his match against Russian rising star Roman Safiullin, sporting a new-look peroxide blond hairstyle.
Tomic told umpire Aline Da Rocha Nocinto at the change-over that he felt he had the illness when trailing 1-2 in the second set.
"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 (to the umpire)."
Tomic expressed surprise that there was no formal PCR testing for players and that only a fast test was necessary.
"They're allowing players to come on court with rapid tests in their room, c'mon ... no official PCR testing," he said.
"Feeling really sick, I'm now back in my hotel room. Just spoke to the doctors on site and they've asked me to isolate. They couldn't treat me yet to avoid contact.
"Thank you for all the support on the court today. I really appreciate it! I'll do better next time. Very disappointed as I really wanted to make Aussies proud and perform well on my home turf."Tomic posted on his Instagram.
During the match, Tomic was attended to by a trainer at the first changeover in the first set, and the player was observed measuring his pulse while on the court.
In the fourth game, the 29-year-old was broken and rapidly surrendered, dropping the opening set in just 23 minutes.
He went on to lose in straight sets in under an hour, 6-1 6-4.
The former world No. 17 hasn't competed in an ATP tournament since September, when he retired in the first round of a Kazakhstan qualifier.