Discussing Milan's win at Fiorentina on Saturday, Galli singled out Leao as a Rossoneri player capable of much more.
He told RAI Radio 1: "Milan, if they find spaces like in Florence, will be a success.
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"Leao is a wonderful player for 10 minutes a game. If he found continuity within the same match, he would be a Ballon d'Or winner. I know Pioli well, he's a extraordinary man and a very good coach.
"In interpersonal relationships he is a magician and always manages to bring out something extraordinary from his players."
He added: "Inter is certainly the strongest in the championship. Milan managed to catch up on Inter two years ago, but this year Inter has had great continuity. There aren't maybe 14 points between Milan and Inter, but everyone is 6-7, Inter remains superior to Milan and all the others."