Benitez spent two years at the Stadio San Paolo, winning the Coppa Italia and Supercoppa Italiana before joining Madrid this summer as Carlo Ancelotti's successor.
And Hamsik has admitted that he did not enjoy the way he had to play under the Spanish coach.
"With the new coach, I have a good relationship," he told Sport. "We often talk about tactics. He is really very picky in that way.
"Compared to the style of football we played under Benitez, he has changed something.
"Why did I find it difficult with Benitez? Last year I played nearly always with my back to the goal, with [Walter] Mazzarri that was not the case."