Marino, who coached him for three months this term before his sacking, is a fan.
"He's a player who I can say a lot of positive things about," Marino told TMW on Monday morning. "He's a really good defender and, above all, a serious professional.
"You can only improve as a player by playing alongside champions. But he is already a Swedish international who knows Zlatan Ibrahimovic well.
"Only the pitch will tell us whether he is good enough to become a starter in the first team or not at Milan, but Granqvist is a player who can only improve."