Zola acted as assistant manager to Sarri as Chelsea won the Europa League and also qualified for this season's Champions League.
“My season with Sarri was difficult, but exceptional in a professional sense," Zola told La Gazzetta dello Sport.
“It's difficult because Sarri has a strong personality, he works very hard and has a high opinion of his own ideas. It wasn't easy convincing him to use different methods when he had to deal with English football.
“It was exceptional because of the way he planned out his work, the focus on details in preparing for games and careful study of the opposition. All that represented an enormous learning curve for me.
“I tried to help him and his Italian staff to relate to and deal with the English culture, so that was my role. When he left, he didn't thank anyone in particular, but that's just what Sarri's like. He is a very reserved man."