The 20-year-old is a third-generation footballer with the club, having followed in the footsteps of his father, modern legend Paolo Maldini, and grandfather, club icon Cesare Maldini, in playing for Milan.
Cesare started his Serie A career at Triestina and ended his playing days at Torino, but Paolo stayed with Milan throughout.
This now represents Daniel's first move away from the club, having made 15 Serie A appearances for the Rossoneri across three seasons. However, those outings have only amounted 194 minutes.
At Spezia, the 20-year-old will get the opportunity to establish himself in the top flight.