Per Football Italia, the tactician also provided an update on Matthijs de Ligt's recovery ahead of Sunday's match: "I don't know if [Ronaldo] can play yet, we'll see what he is able to do today and also tomorrow morning. It's nothing serious, just a pain in his knee that then leads him to unbalance his posture during games. Matthijs de Ligt had a positive response to tests on his ankle and we'll see today, as he'll train with the squad."
De Ligt missed out on the 2-1 win over Lokomotiv Moscow in the UEFA Champions League in midweek, while Ronaldo was substituted in the second half.
After the match, Sarri explained to reporters he made the change because the 34-year-old's knee has been bothering him.
The switch worked out, with Gonzalo Higuain setting up Douglas Costa for a late winner.
Higuain spent the first half of last season on loan at Milan, making Sunday's match against the Rossoneri a special one for him.
Sarri believes the added motivation could lead to good things "Gonzalo's history shows he needs strong motivation to give his best. He is currently in good shape both physically and psychologically, so he can and is giving the team a great contribution. He's really helping in the build-up, I feel he can do a tiny bit more in the finishing, so should go for goal himself more."
Sarri also said Leonardo Bonucci won't be rested, with the team's defence incapable of surviving without him. The 32-year-old has been an automatic starter since Giorgio Chiellini went down with an injury in August, mostly pairing with De Ligt in the heart of the defence.
He played next to Daniele Rugani in Moscow, but football writer Adam Digby felt that did not work out well:
De Ligt will likely replace Rugani on Sunday if his ankle is sufficiently healed. Rugani has made two starts so far this season and disappointed in both, but he is the most experienced option off the bench. Merih Demiral hasn't received any playing time since the 2-1 win over Hellas Verona in September.
Costa was the hero in Moscow and is expected to make his first start since August on Sunday. The Brazilian missed nine games because of injury, and adding his creativity and athleticism will boost Juventus.
Milan have won just four of their 11 Serie A matches so far and started the weekend in 13th place. Juventus came into the weekend in the lead, with Inter Milan one point behind. The Nerazzurri will face Hellas on Saturday.