The 23-year-old has been in talks over a return to his homeland, with a fee of 15million euros (£12.2m) reported in Italy.
His representative Gilmar Veloz told Brazilian radio network Radio Bandeirantes: "Milan gave the okay to the transfer, we are defining the details. Nothing can hinder the successful conclusion of the deal.
"It is a large transfer which concerns a good young player and Corinthians are making a big effort."
Pato quickly established himself as a favourite at the San Siro after signing from Internacional in 2007, scoring nine goals in his first half-season and reaching double figures in each of the next three campaigns.
However, he scored only once in Serie A and four times altogether last season and has made only seven appearances in all competitions so far this term.