Barca host Napoli in the first leg of their Europa League tie on Thursday evening at the Camp Nou.
Araujo suffered a muscular problem last weekend in the derby draw with Espanyol and hasn't been able to recover in time, having been taken off at half time then. He is yet to return to training with his teammates.
The Blaugrana are due to train again on Thursday morning ahead of the game, but it's not an intense session and is more of a warm-up activity, which Araujo won't take part in.
Barcelona will also be without both Clement Lenglet and Samuel Umtiti at Mestalla.
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