Juventus welcomed back Dusan Vlahovic after three months and had Paul Pogba on the bench, but lost Arkadiusz Milik to a new muscular injury.
The Bianconeri saw their season go from bad to worse with this home defeat to Monza, who had already beaten them 1-0 at the U-Power Stadium back in September.
Max Allegri thought the injury crisis was finally starting to abate with the return to the squad of both Vlahovic and Pogba for the first time in 2023.
Vlahovic even managed to come on for the final half-hour, his first appearance for his club since October 25.
However, there were new problems for Allegri, as Arek Milik pulled up with a thigh injury and limped off with 10 minutes to go.
All the substitutions had been completed by that point, so Juventus saw out the match down to 10 men.
It remains to be seen how serious the setback is and if he will also be out of the Coppa Italia quarter-final with Lazio next week.