 He played a key role during Milan's 1987–88 Serie A triumph, as Milan only conceded 12 goals in 30 league games, finishing with the best defence in Italy.However, due to injuries, and the emergence of Alessandro Costacurta in his position, he began to find less space in the starting line-up, and was usually used as a substitute in later years, although he was still able to contribute to important victories with the club, notably helping Milan to keep a clean-sheet with a dominant defensive performance, as they defeated Barcelona 4–0 in the 1994 UEFA Champions League Final.Before joining the Milan senior side, Galli initially made his professional debut whilst on loan with Pescara during the 1982–83 season.