Luka Jovic and Christian Pulisic struck for Milan, with Robert Lewandowski netting twice for Barca. The Rossonero won the preseason friendly on penalties.
Fonseca later said: "I am satisfied with my players, they often played with courage. We had a good approach to the match, in the first 20-30 minutes we did several good things. It was a match in which we also had some difficulties, they are strong, but in general I am very satisfied. I saw the intentions of the team and the courage of the players.
"We need to improve, but we have done some good things in these three friendlies against strong teams. We want to quickly recover the ball when we lose it. We want to be a team that presses high. We're starting to see the high pressure from the team, clearly we have to improve, but it will be one of the things we want to do on the pitch."
On the US tour, the Portuguese explained: "They have been very good days. The people and the fans have been special to us. Now it's time to go home, we will have two days to be with our families and then we will start preparing the first official match, even if we have another friendly against Monza first.
"We have to start thinking about the debut in the championship, we will play the first at San Siro, I expect the stadium to be full. We want to build a team that will leave the fans proud. We started well, we have to improve, but in the end I think the fans will always be with us. We want to feel their support from the first day."