The Ibrox playmaker has caught the virus whilst on international duty with Romania and has been ruled out of their match against North Macedonia in Skopje tomorrow evening.
Hagi, who featured in the win over Liechtenstein in Bucharest on Sunday, is now isolating along with three Romania teammates who are awaiting results of an official PCR test.
A Romanian FA statement read: "Today, around noon, Ianis Hagi complained of slight headaches in the Skopje national team's camp.
"He performed a quick test under the coordination of the medical staff of the national team and the result is positive.
"The Romanian squad immediately went into isolation. To date, on the occasion of this action of the national team, Ianis had performed 5 COVID tests, all with a negative result.
"Thus, they performed a PCR test, the result will arrive by game time.
"Without showing symptoms, Hagi's colleagues, Răzvan Marin, Alexandru Cicâldău and Dragoș Nedelcu also performed a quick test. The result is negative for all three.
"However, the three will not be able to participate in the official training tonight, as according to the rules of Northern Macedonia, a negative result of a PCR test is necessary in such a situation."
The positive test will rule Hagi out of Rangers trip to St Johnstone on Saturday while a 10-day isolation would also put him out of the Europa League group opener against Lyon at Ibrox next Thursday.