What authorities have said so far...

Victoria's Department of Health said further testing was being done to confirm the positive result.

"Until that time, the Department is treating this as a positive case and acting accordingly.

That includes getting the man to isolate at home, interviewing him and close contacts, and calling on people to come forward and get tested if they have any symptoms.

"The department is working with interstate counterparts to determine the likely source of this infection," a statement said.

SA Chief Public Health Officer Nicola Spurrier said the man could have acquired the virus in quarantine or may have caught it overseas and simply had a longer-than-usual incubation period.

"The next possibility is that there's something that's happened in our hotel quarantine system and this person has managed to acquire the infection or catch COVID whilst in the hotel setting," she said.

"This new case in Victoria was in a room at the Playford medi-hotel alongside another traveller who was one of our cases."

Professor Spurrier said the man did not appear contagious while in the Playford medi-hotel and investigators are looking at CCTV footage from the hotel to see if there is any evidence of transmission.