Vincenzo Montella has kept AC Milan in contention this season despite a catalogue of issues and distractions to deal with.
Forward told Mediaset that negotiations should be concluded within a week and added: "There's very little left to do -- we are very close."
De Laurentiis held talks with Manchester United forward Inrahimovic before he opted to move to Old Trafford.
Napoli goalkeeper Pepe Reina said his team could still turn the tie around following their 3-1 defeat at Real Madrid in Wednesday's UCL first leg.
Cassano was released from his contract at Sampdoria last month, and the 34-year-old has turned down offers from both China and Serie B.
Ex-AC Milan and Italy manager Arrigo Sacchi says that Napoli coach Maurizio Sarri is a "genius" and the "most important" factor for his team.