Test results have shown muscular lesions for both Napoli players Alex Meret and Mario Rui, adding to the problems for new coach Walter Mazzarri.
The goalkeeper was already struggling with a calf issue and pulled out during the warm-up of last week’s 1-0 home defeat to Empoli.
He then withdrew from international duty with Italy and tests have confirmed a Grade I lesion to the tibial muscle in the left leg.
Mario Rui sustained an injury during that Serie A match against Empoli and limped off the field.
He has been diagnosed with a medium lesion to the adductor in the left thigh.
Of the two, Mario Rui has the more serious injury and is expected to be out of action for at least three weeks.
Meanwhile, Victor Osimhen was expected to make his comeback from a thigh injury sustained playing for Nigeria over a month ago.
However, he was absent from the training ground after coming down with flu symptoms.