If confirmed, it would be the second such case in about three months.
The 32-year-old office worker, who had not been vaccinated, had his coronavirus-positive throat swab taken at a clinic in South Horizons on Monday.
His samples have tested negative since he was admitted to hospital, and he was asymptomatic.
Samples taken from some 30 close contacts have also shown no traces of Covid-19.
University of Hong Kong microbiologist Yuen Kwok-yung, who inspected the South Horizons clinic with other health officials, said staff there used the same desk to collect samples and administer Sinovac jabs.
“The doctor had completed all the disinfection procedures properly. He had immediately washed his hands every time after taking swab samples or giving vaccine injections, but you know the ribonucleic acid did not disappear after wiping the desk with alcohol,” he explained.
Yuen said swab taking and vaccination should be done in separate rooms, and if that’s not possible, the environment has to be cleaned with bleach every time after use.