Arsenal’s squad for the game against Chelsea was announced and there was much consternation when Gabriel was not included but it turns out he is in self-isolation, not that we need to worry, running out 3-1 winners.

Naming Gabriel Martinelli and Emile Smith Rowe in the starting lineup for Arsenal’s showdown with Chelsea on Boxing Day, there was no sign of Gabriel, David Luiz or Willian.
Nobody cared much about the latter two but Gabriel has been one of Arsenal’s best performers this season.
So where is he?
Turns out he’s in self-isolation:
In what is another cruel blow, Gabriel will now miss the next three matches.
David Luiz and Willian both felt unwell and are also isolating but have tested negative.
https://twitter.com/Arsenal/status/1342876201703141376
Arsenal squad vs Chelsea:
Leno, Bellerin, Holding, Mari, Tierney, Elneny, Xhaka, Saka, Smith Rowe, Martinelli, Lacazette
Subs: Runarsson, Cedric, Mustafi, Maitland-Niles, Ceballos, Willock, Pepe, Nketiah