Doctors have worried for months about the pandemic reaching the northwest, Syria's last big rebel bastion, where an army offensive uprooted around a million people earlier this year.
The person infected is a physician at Bab al-Hawa hospital near the Turkish border, said a report from the Assistance Coordination Unit (ACU), a group which delivers aid and belongs to the Syrian opposition.
He isolated himself as soon as he showed symptoms this week and anyone who came in contact with him will be tested, said the ACU, which has received Western and Turkish Backing.
Aid workers have warned that any outbreak in the crowded camps for the displaced would be lethal and fast. The tented makeshift settlements often do not have clean water, let alone space for social distancing.
Test kits have also been scarce.
The UOSSM medical charity, which operates in rebel territory and also reported the case, warned the virus could "spread through refugee camps like wildfire.""The medical infrastructure cannot handle the existing population needs let alone a wide spread pandemic," it said in a statement.