Maurizio Sarri is Napoli's 'most important' factor - Arrigo Sacchi

Ex-AC Milan and Italy manager Arrigo Sacchi says that Napoli coach Maurizio Sarri is a "genius" and the "most important" factor for his team -- and could guide them to a surprise in Wednesday's Champions League last 16 first leg at Real Madrid.

A former amateur player and banker, Sarri began coaching part-time in regional Tuscan leagues, and has since worked his way up over 18 clubs in 25 years to reach Napoli -- where he has impressed hugely during his first 18 months in charge.

Decades earlier Sacchi took a similar path to success at the top level where he won two European Cups with Milan, and told Marca that Sarri's ability to improve players and get them playing as a team was extra impressive.

"Sarri is the most important of all," Sacchi said. "He has a great ability to teach. [Gonzalo] Higuain scored 36 goals with him, which you do not see much in Italy. He left, and now the team are scoring even more as a whole.

"Sarri is the strength of the team. He is the director and author of the orchestra, all the players have improved under him. [Dries] Mertens, for example, used to never score goals, now he has 14 or 15. When you see Sarri's teams play, you know how they train. He is a genius. When I was technical director with the Italy youth teams, I always went to watch kids in Serie B, and I was already impressed by his Empoli."

Sacchi said that when Sarri was impressing at previous club Empoli he had recommended him as an option to Milan president Silvio Berlusconi, who now regretted not having taken that advice.

"Two years ago I said to Berlusconi: 'Silvio, if you want repeat with Milan what happened with me 25 years ago I will give you a name. It won't cost you money, but he is the coach you need, he looks after the players, they understand him,'" he said. "I know they were talking, then Galliani stopped it and I don't know why they didn't like him. Last year Silvio told me -- Arrigo, I was wrong."

It would be a big test at the Bernabeu with such an inexperienced team, but Madrid would likely underestimate their lower profile opponents, said Sacchi, who had an unhappy short spell as sporting director in the mid-2000s.

"It is a very young team, without experience, and we will have to see how they manage the occasion," he said. "Two years ago [Amadou] Diawara was being relegated to the third division. Almost none of them have played at the Bernabeu. But I think Madrid do not see Napoli as a real rival, and that is a mistake. Remember that."

Napoli's strength as a team was how well organised they were in attack, but their forward players should work harder off the ball, Sacchi said.

"They have pace, skill, they move together," he said. "They play good football. They do not have top players but they are very well organised. With the ball they are very good, without the ball they suffer more in the defensive phase. The problem is that those up top do not always press strongly, and that causes problems for those behind."