The deal is technically a loan with option to buy, but the option should become an obligation after the French club earn their first point.
“I arrived in Naples in the summer, it was 2016, over four years ago, but I will never forget my first impact with the city," said Milik in a video of him walking along the waterfront.
“Naples has this effect: it welcomes you, embraces you, it makes you feel at home, which is how I have always felt here.
“There were times I cried over these four years. With pain, when I was injured. With sadness, when we came so close to the Scudetto. With joy, after the penalty in the Coppa Italia Final.
“But for all that time, even during the most difficult times, there was only one certainty: the warmth and affection of the Neapolitan people.
“You applauded me, you learned my name, you waited for me when I was hurt. You criticised me when I made mistakes, but you were always with me.
“I leave now, but I bring with me a piece of you, I put it in my luggage. From close or far, I will never lack respect for these colours or this city.
“I leave the way I arrived, with a smile, because I know what I gave and what this city gave me. An embrace to you all."