The Poland international missed the majority of last season after suffering a torn anterior cruciate ligament.
He is now fully recovered and has taken part in all of the club's pre-season training but his firs-team spot is not guaranteed.
During his absence, Dries Mertens established himself as a regular striker and his form helped Napoli finish third in the Serie A table.
While Milik is hoping to move to the Ligue 1 giants, Napoli are determined to keep hold of him.
If they qualify for the Champions League, Milik is expected to stay put but he is determined to experience a new challenge.