The 31-year-old started Barca's 1-0 La Liga win at former club Valencia on Sunday, before being substituted with just over 20 minutes remaining.
And Barca confirmed on Monday that Matheu was absent from training after being struck down by illness.
"Jeremy Mathieu... was unable to take part in Monday morning's training session due to a virus," read a club statement.
"He will return to action as soon as he is feeling better."
Barca's victory at Valencia was sealed by an injury-time winner from Sergio Busquets, with the Catalan club's attentions now switching to Wednesday's Copa del Rey round-of-32 first leg against third-tier Huesca.
Coach Luis Enrique will have a full squad to choose from for the game at Estadio El Alcoraz, with the possible exception of Mathieu, who seems likely to be rested.
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