Despite failing to win a trophy at the club, Sarri's Napoli were praised for their expansive and attractive attacking football
Hamsik, among many others, flourished under the 59-year-old at the San Paolo Stadium during his three years at the club.
"Sarri is a man who belongs on the field, he lived the game 24-7," Hamsik told Corriere dello Sport.
"He was a sick man.
"He was obsessed with football and never even let the slightest detail get by him.
"What has improved me the most, has made me evolve technically and tactically, is Mr. Sarri.
"We are all happy with [Carlo] Ancelotti, as in a few short weeks he showed us that he is a wonderful, open person.
"He gives us a lot of advice, is good fun and it's no coincidence he has won everywhere he went in his career.
"Everyone is a little sceptical after the summer friendlies, but we saw in the win against Lazio how much grit we bring to the table in competitive games.
"Napoli are still a good side that wants to play football and entertain the fans. We haven't won much, so far, but we really want to."