Agent Fabrizio De Vecchi can see Napoli allowing Arek Milik to run down his contract.
The Poland striker's deal expires in June.
"Arek has thought about his future for long time," De Vecchi told AS.
“He was very attached to his teammates and to the city, but in the end he decided to leave. A 26-year-old has the right to make such choices at this stage of his career.
“He acted as a real professional. He's been training, sometimes even twice a day. Napoli left him out of their squad and our lawyers are analysing the club's behaviour with him."