Chelsea sold Christopher Nkunku to AC Milan in September for €42m, a deal that is increasingly looking beneficial for the Blues.
Nkunku, the France international, has failed to prove himself, offering little value to the Rossoneri, and is yet to start a Serie A match or score a league goal.
He has become a 'complete problem' for the team, according to MilanLive.
Author's summary: Nkunku's transfer to AC Milan has not paid off.