Christian Pulisic only managed one goal in his final season with Chelsea
Pulisic, 24, is surplus to requirements at Stamford Bridge and is due to have a medical in Milan this week.
He joined Chelsea from Borussia Dortmund in a £57.6m move in 2019 that made him the most expensive player from North America.
Pulisic scored 26 goals in 145 games and played in the 2021 Champions League final win over Manchester City.
His switch to Serie A will mean linking up with former Chelsea team-mate Ruben Loftus-Cheek, who has also joined Milan this summer.
Meanwhile, Chelsea striker David Datro Fofana, 20, has made a season-long loan move to Union Berlin in the Bundesliga.
The Ivorian made just four first-team appearances for Chelsea following a January move from Molde.
Chelsea have parted ways with several established first-team players this summer.
The departures have included Kai Havertz moving to Arsenal, Mateo Kovacic joining Manchester City and Mason Mount making the switch to Manchester United.
Cesar Azpilicueta joined Atletico Madrid, while other exits have seen Kalidou Koulibaly go to Al-Hilal, Edouard Mendy sign for Al-Ahli and N'Golo Kante leave for Al-Ittihad.
-- Courtesy of BBC Sport