The Dutchman played for both clubs.
"Barca are on another level," the 36-year-old told Mundo Deportivo. "They are the absolute favourite for the Champions League and bad things would have to happen for Milan not to be eliminated.
"Milan are certainly a good team and will forever be competitive. The Italian League is difficult, but Barca have too much for them and I would say that about any team.
"Milan have lost two very important pieces, Zlatan Ibrahimovic and Thiago Silva. Barca instead have maintained the same structure as the winning team with Pep Guardiola. Nothing seems to have changed with Tito Vilanova.
"In fact, the way they play has the same basis as the first year of Frank Rijkaard, which was also my last year at the club."