Leao broke the deadlock in the 37th minute with a stunning shot into the roof of the net from a low cross by Ismael Bennacer, who won the ball around the halfway line and dribbled past Girona’s midfield to set up the Portugal winger.
Girona’s Spain forward Bryan Gil thought he had scored an equaliser before the hour mark with a lovely curled shot inside the far post, but his effort was ruled out for offside.
Milan are sixth in the standings on 15 points with the top eight earning automatic qualification for the last-16 stage. Debutants Girona, who have a single league phase win, are 31st with three points and have no chance of securing a spot in the playoffs.
