The 22-year-old was subjected to the compulsory Portuguese government medical test on arrival in the city of Guimaraes from the Black Stars training camp in Turkey where they played two friendly matches.
Gideon Mensah becomes the third Ghana national team person to test positive for the coronavirus following the Black Stars friendly matches against Mali and Qatar in the past seven days.
The result of the test confirmed that the right-back had contracted the virus while on international duty with the Black Stars and has been put under mandatory quarantine.
However, what cannot be confirmed is if Gideon Mensah got the virus on his journey from Turkey to Portugal.
He is expected to isolate himself for the next two weeks before he can rejoin his Vitoria Guimaraes team-mates but not until tests have confirmed him to have overcome the deadly virus.