NSW Treasurer Dominic Perrottet is in isolation after being identified as a close contact of the Sydney man diagnosed with a mystery COVID infection on Wednesday.

Mr Perrottet said on Thursday he went into isolation on Wednesday night after learning of the potential contact.

He was at the District Brasserie, in Sydney’s CBD, on April 30, at the same time as the man in his 50s from the city’s eastern suburbs whose positive virus test has sparked alarm across NSW this week.

Mr Perrottet said his coronavirus test has come back negative, but he would keep isolating for 14 days from April 30, in line with NSW Health requirements.

The Treasurer, 38, attended NSW Parliament on Tuesday and Wednesday.

Elsewhere, Sydney Roosters players have also been sent for virus tests and staff told to stay home after the infected man visited the Azure Cafe on Monday, less than 100 metres from the NRL club’s Moore Park headquarters.

Players were rushed in for tests on Thursday, ahead of Friday night’s match against Parramatta.

The main concern centres around the infected man’s visit to the Azure Cafe on Monday, less than 100 metres from the Roosters’ headquarters.

The cafe is a popular coffee stop and lunch venue for both Roosters and Sydney Swans AFL players, as well as sports officials.

It’s believed, however, that no Roosters were in the cafe at the time of the infected man.

NSW Premier Gladys Berejiklian has said she expects more local virus cases after the man’s diagnosis on Wednesday.

• See the latest NSW Health venues of concern here

The man’s positive result was recorded on Wednesday morning but NSW Health believe he has been infectious since last Friday. The source of his infection remains a mystery.

The man, in his 50s, spent several days visiting restaurants, shops and other venues across Sydney before feeling unwell and getting tested for COVID.

“We have to assume there’s other cases and our response will be proportionate as it always has been in NSW,” Ms Berejiklian said.

“Everybody in the state needs to be on high alert.

“Anybody anywhere with the mildest of symptoms needs to come forward and get tested.”

One of the man’s family members has tested negative for the virus, with results pending for his other family member.

NSW Health contract tracers are working to identify the man’s other contacts and genome sequencing is underway. Results are expected on Thursday.

-with AAP