Striker Mario Balotelli is to undergo surgery on his injured knee that could rule him out for up to six weeks.
Roberto Mancini's summer capture from Inter has flown back to Milan with key Barclays Premier League clashes against champions Chelsea and top-four rivals Arsenal looming at City of Manchester Stadium.
Balotelli, who damaged the knee during his scoring debut against Timisoara in Romania last month, will also miss the Europa League group home game against his old rivals Juventus.
The Italian's injury is to the lateral meniscus, one of the two most crucial structures in the knee, and medical wisdom is to try and encourage the problem to heal without recourse to an operation.
It was hoped that the symptoms would settle down but once Balotelli began to step up his recovery programme this week, it became clear that action would need to be taken.