The defending champions have stumbled in recent weeks, including defeat to Udinese on the weekend.
Sacchi told La Gazzetta dello Sport: "The Rossoneri, Inter, and Napoli have shown their flaws. Nothing stops Roma from entering the Scudetto race; there's time to do so.
"I explain (Napoli coach Antonio) Conte's ups and downs like this. The Azzurri, when they play well, have a more European style, while the Nerazzurri are a bit shaky at the back, even though they have a lethal attack.
"Then there's Milan, who are very solid."
On Milan, he added: "Why have they dropped so many points against small and medium-sized teams? They need to work hard, especially defensively."
Sacchi doesn't shy away from predictions either, declaring that Napoli are the favorites, ahead of Inter and Milan.