The Brazilian came into close contact with someone who has tested positive for Covid-19 is now has to self-isolate.
It is a blow for Mikel Arteta, who will now be without one of his key players for a crucial period as Arsenal bid to turn their season around after a dismal run of form.
Gabriel has been a regular in the Arsenal defence since joining in a £27million deal from Lille over the summer.
Speaking before the Chelsea match, Arteta said: “Gabriel was in touch with someone who tested positive so, following the protocol, he is out.
“It is what it is. In this Covid world, this can happen to any team. It has happened to us now in a really bad timing, but that is why we have other players.”
Fellow Brazilians David Luiz and Willian also miss the Chelsea game because they are unwell but they have both tested negative for Covid-19.
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