The 27-year-old is strongly connected to a move to Old Trafford despite Luke Shaw, Patrick Dorgu and Harry already gather in their team.
For each journalist Matteo Moretto, AC Milan has now introduced negotiations with Brighton for Estupiñán while setting up their search for a replacement for Theo Hernandez.
However, no official offer has been made, but Milan would like to get the deal quickly over the line to beat Man United.
Estupiñán will enter the last year of his contract with Brighton in the 2025-26 season without conversations about a new deal from still.