Matteo Gabbia cut short Tuesday's training session at Milanello with an ankle problem and is now a doubt for the Juventus match.
The timing sharpens the worry more than the injury itself does. Milan's central defence has been under scrutiny for weeks over whether the numbers add up, and losing an option for a fixture like this one only feeds that debate.
According to MilanNews, Gabbia picked up the issue in training on Tuesday, described as more of a nuisance than a serious problem. He was given specific treatment and will use Wednesday's scheduled day off to try to recover.
It is not being treated as a cause for concern, but the situation needs watching given how thin the position already looks. Gabbia had been competing with Koni De Winter for the central centre-back role.
Mario Gila and Strahinja Pavlović are the other starters, and with Fikayo Tomori out of the plans, the depth behind them runs to the young pair of Sankoun Diawara and Valeri Vladimirov. They are the next names in line should an injury bite.
From here, the coaching staff will judge how Gabbia responds to treatment before deciding whether he features against Juventus.