Fullkrug joined Milan at the start of the January transfer window on loan with an option to buy, believed to be around €5 million. At the time, Milan were without a "true" central striker due to Santiago Gimenez's injury, and manager Massimiliano Allegri often opted for a combination involving Rafael Leao, Christian Pulisic, or Christopher Nkunku.
Since arriving at Milan on January 2nd, the German has played 16 matches for the Rossoneri but has only started three times. His only goal for Milan came in a 1–0 home win against Lecce on January 18th in Serie A.
According to the latest reports, this performance has not been enough to convince Milan to spend €5 million to make Fullkrug's transfer permanent this summer.
Fabrizio Romano reports that Fullkrug will be returned to West Ham at the end of the 2025/2026 season, and the Premier League club will look to loan him out again.