The English midfielder who signed from Chelsea in June, has made an impressive start to his Milan career, but has missed the last two games through injury.
"We won't have Loftus back because although he has recovered from the muscle injury he had, he's not yet 100% to be with us," Pioli told a press conference ahead of Sunday's game. "But I hope to have him back in the next games."
Milan do have two players returning from injury, defender Pierre Kalulu and Bosnian midfielder Rade Krunic, but will be without Nigerian forward Samuel Chukwueze who suffered a hamstring injury on international duty.
Pioli needs to decide who will take Chukwueze's place on the right side of attack.
"The best alternative is certainly (Luka) Romero who is doing very well. I will be very happy if he finds space in these matches due to the way he is training.
"I'm very calm if (Christian) Pulisic has to rest, because Romero is definitely ready. (Yunus) Musah could also play there, with other characteristics."
With keeper Mike Maignan suspended, the injury to reserve keeper Marco Sportiello means 40-year-old Antonio Mirante gets his first start since joining the club in 2021.
"I have the utmost trust in Antonio. He is an expert, a reliable goalkeeper, fully involved in what we are doing, and is respected by his team mates for his technical and moral qualities.
"There is no need to say much to a player so experienced and ready to make his mark on the game tomorrow."
Milan host Juventus at the San Siro, with Juve four points behind the leaders in third place. Inter Milan are away to Torino on Saturday and are in second spot two points adrift of Milan.