The Ho Chi Minh City Center for Disease Control said the man, 35, works for an auditing company on Pasteur Street, District 3.
He visited Vinmec Hospital on Monday for suffering symptoms including fever, coughing and sore throat.
His first test arrived as positive on Tuesday and the source of his transmission remains unknown for now.
He has not been recorded as Covid-19 patient, pending further test results from the HCMC Hospital for Tropical Diseases.
Healthcare workers have been sent over to Sunview Town to collect samples of local residents.
For the ongoing Covid-19 wave that broke out in Vietnam three weeks ago, HCMC has recorded just one case on April 29. The patient is a man from the northern province of Ha Nam who was visiting relatives in the city when he tested positive. He had come into contact with a Ha Nam man who had returned from Japan and was later found to be infected.
Until then the city had gone 75 days without local transmission.
Nationwide, 1,340 cases have been recorded in 28 cities and provinces so far in this wave.