AC Milan made the mistake of including Stephan El Shaarawy as one of its 'A list' players when it could have classed the Italy international as a 'B list' player.
AC Milan director Umberto Gandini has taken responsibility for the blunder that has robbed M'Baye Niang of the chance to represent the club in this season's Champions League group stage.
The Rossoneri finalized their 25-player squad Tuesday but made the mistake of including Stephan El Shaarawy as an "A List" player when the Italy international could have been named in the "B List," thus creating an extra spot for Niang.
"Umberto Gandini regrets this error and apologises to all parties concerned, as well as professionally to the Rossoneri fans."
Niang is therefore ineligible for Milan's Group H clashes with Barcelona, Ajax and Celtic.