Mehdi Benatia is likely to be out of action for the next three weeks after picking up a thigh strain in Udinese-AZ Alkmaar.
The defender already had heavy strapping to his left thigh when he pulled up suddenly during Thursday’s Europa League match.
He has been diagnosed with a strain to the top of the thigh, where it meets the groin muscles, and is expected to be sidelined for three weeks.
Dusan Basta is also on the treatment table with Mauricio Isla, so Damiano Ferronetti could step in against Napoli.
Danilo also returns from suspension.