Fonseca's appointment was confirmed this morning.
Ibrahimovic said today: "He will be the new coach, it was a thoughtful choice. We want Milan to be able to play dominant football. We studied how he trains, how he prepares matches. After five years, we needed something new.
"Fonseca is the right man, we believe in him so much. He is the right man."
Milan's three stars Rafael Leão, Mike Maignan and Theo Hernández have for some time been linked with departures this summer. But all three look set to stay.
"Theo and Maignan will stay, Leão too. They are among the strongest players in their roles and have contracts with us, they are happy. We don't need to sell. Thanks to RedBird's work, we can bring in strong players to improve the squad," says Ibrahimovic.
"The next step is to strengthen the team, to become more competitive. We want to win trophies, in Italy and in Europe, because we are Milan. The ambition is to fight for trophies every year. Milan don't just win, Milan make history. Whoever joins Milan must have the same ambition."
On replacing Olivier Giroud, now of LAFC, Ibrahimovic raised the name of Bologna's Josh Zirkzee.
He stated: "Last year, Milan did a fantastic transfer market, we needed to lay the foundations. Above all, this market will focus on details. After Giroud's departure, we need a new 'nine'. (Luka) Jovic is there, but we are looking for a new striker.
"Zirkzee is a strong player, he is coming off a great season. He comes from the Netherlands, whether he is a new 'Ibra' or not... there is a big difference between reality and what is said and written."