After Milan were unable to sign the former Madrid striker Alvaro Morata, it seems that, according to Calciomercato, the Rossoneri have set their sights on current Chelsea striker Diego Costa. Costa publicly expressed his desire to leave Chelsea after a fallout with Antonio Conte and made it clear he wants to transfer to Atletico Madrid. However, Atletico is banned from signing any players until the January transfer window, and Costa can't afford to be benched for that time.
Thus, Costa wants to be loaned to a club but only for a six month period. Milan wants Costa on a permanent deal or at least on a season long loan. When asked about Diego Costa Milan's general manager Marco Fassone Commented:
If Costa is signed, the Spaniard would probably play alongside Andre Silva and undoubtedly send Carlos Bacca to the bench (if Bacca is even still on Milan). For now, though, Fassone couldn't have said it better—Costa is indeed a Chelsea player.