The city rivals meet at San Siro ninth and 10th in the table after respective seasons of struggle.
Defeat for either will likely see their faint chances of European qualification go up in smoke and Rossoneri coach Filippo Inzaghi has been handed a headache, with Lopez reported to have injured a finger in training this week.
Veteran Christian Abbiati will likely fill in if the former Real Madrid man cannot recover his fitness.
Inzaghi has been boosted elsewhere on the pitch, however, by Mattia Destro's return to training on Friday.
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