But 15th-placed Arsenal say, despite “feeling unwell” fellow center-back David Luiz and midfielder Willian also tested negative.
On Thursday, the pair will begin outdoor preparation, having sat out the shock 3-1 home victory over former club Chelsea on Saturday.
In a tweet, Arsenal stated that Gabriel “has tested positive for Covid-19 and is isolated under the protocols of the UK Government and Premier League.”
“Giving support to Gabriel and watching him how he grows is our top priority, and we hope he’ll be available to play again after our next 2 matches.”
Since entering into self-isolation for making intimate contact with someone who tested positive, he was absent against Chelsea.
Since his summer arrival from Lille, playing 15 games, the Under-23 international has become a rare success story for the struggling Gunners.
And manager Mikel Arteta said of the Gunners’ coronavirus issues before the Chelsea clash: “It is what it is.”
This could happen to every team in this world of Covid, and now it [has] happened to us at a really bad time.
“It’s for every other player to step up and fill in the gap. [They] will try their best and fight.”
The Gunners, meanwhile, are ranked favourites to sign Tariq Lamptey, should Brighton sell the defender in the transfer window of next month.
Barcelona was also linked to the 20-year-old whose decision to leave Chelsea for more routine Prem football in January seems to have been vindicated.