Antonio Nocerino rushed through a deadline-beating transfer from Palermo to Milan.
The Italy midfielder had already been linked last week after Mathieu Flamini was ruled out for five to six months by a knee injury.
The Rossoneri repeatedly assured their market was completed for the summer, but Nocerino has been added to the squad minutes before the deadline.
Milan have bought Nocerino on a permanent basis in exchange for an undisclosed fee, thought to be just €0.5m, plus co-ownership of youngster Ricardo Ferreira.
The player signed a five-year contract that was registered with the Lega Calcio just minutes before the 18.00 UK time deadline.
Nocerino would've been out of contract with Palermo in June.
Think you know your Italian football? Share your knowledge, tips and comments to win cash prizes in OLBG's World Cup tipster competition  - £10,000 to be won!