Balotelli out for Lazio clash
Balotelli was injured in last weekend's derby when he collided with Inter goalkeeper Samir Handanovic.
Milan coach Massimiliano Allegri says Balotelli hasn't been able to train all week because of the bruise.
The club did not specify which leg it was.
Since transferring from Manchester City last month, Balotelli has scored four goals for Milan.
Fellow forward Stephan El Shaarawy was included in Milan's squad, having recovered from a fever.
Milan is two points behind Lazio in fourth place.