The former Italy coach has been impressed by Napoli's work in the market this summer.
Manchester City legend Kevin de Bruyne has arrived, while deals for Bologna defender Sam Beukema and Udinese striker Lorenzo Lucca are also close.
Sacchi told La Gazzetta dello Sport of De Bruyne: "(Antonio) Conte has chosen a true professor. De Bruyne was formidable at (Pep) Guardiola's City and will be very important at Napoli too. He's a serious player who doesn't come here to just hang out. He wants to get involved, and the Napoli environment has completely captivated him."
On Beukema, he also said: "A great centre-back. Quick, alert, good in the air, always ready to anticipate. Beukema was a key player at Italiano's Bologna and will become one at Napoli too. With a player like that, you can even think about defending a little further forward, without having to drop too deep."
And on Lucca, Sacchi added: "He's a tower who could be used to replace (Romelu) Lukaku. It seems to me that Napoli is moving towards building a team capable of competing in the league and the Champions League. And participation in the cup, in my opinion, is the real unknown factor in Napoli's season. International matches sap a lot of your physical and psychological energy.
"Inevitably, you drop a few points in the league."