Leonardo had a big say in the landing the 17 year-old and told Milan Channel: "I am happy, as I think this is a signing that can give everyone a lot of joy.
"It was a good transfer operation in true Milan style, involving everyone. I am really glad for the boy and for Milan."
Leonardo returned to the San Siro club this summer as a transfer consultant after a spell working as a television pundit in Britain, Italy and Brazil.
"Milan have a structure and atmosphere that help us and I am only part of that," said the modest World Cup winner.
"Pato will find many Brazilians here who will help him and his family is very close to him, as is normal for a 17-year-old. There are a series of elements that will aid his passage to Europe.
"Many clubs observed him and when Milan track a player, other sides pay a little more attention. But his agent was also convinced from the start that Milan were the right destination.
"Milan manage to win players over and that atmosphere, that air of victory, really helps transfers to reach a conclusion.
"I think that Pato also understood this is why Milan is the place for him. This is such a stable club, it gives players the ease of mind and protection to develop. That is crucial."