Pato had played only 26 professional matches, yet was costing the European champions £15million.
Italian FA rules meant that as a non-European Community teenager, Pato could not play in Serie A until he turned 18, which left the Brazilian missing the first half of the season.
"Pato is certainly better than Ronaldinho and Milan won't need to make any moves to Barcelona to sign him now that people have seen what Alex is capable of," beamed coach Carlo Ancelotti after his debut against Napoli last month.
"He's literally a phenomenon with startling speed, a powerful shot and that elusive sense of where the goal is that only the top, top strikers have."
Kaka agreed. "He's a great footballer already and also a strong personality," he said. "Alex has a capacity to dribble which very few guys possess but he also has the killer striker instinct of always looking to score himself."