The game will take place on August 15, not long before the Premier League season starts later that month, with United looking to build on last term's encouraging third-place finish under manager Michael Carrick.
United open their pre-season against Wrexham in Helsinki on July 18 before facing Rosenborg in Trondheim, Norway the following Friday.
They then play two fixtures in Sweden, taking on Atletico Madrid in the Snapdragon Cup in Stockholm on August 1 and European champions Paris Saint-Germain in Gothenburg one week later.
The Red Devils face bitter English rivals Leeds in Dublin on August 12 before completing their pre-season campaign against Italians Milan three days later.
"We're excited to be concluding our pre-season tour in Wroclaw, Poland, with a big game against AC Milan," director of football Jason Wilcox told United's website.
"With fixtures now confirmed across five countries and six fantastic cities, these matches will provide strong preparation for the 2026-27 season and a valuable opportunity to connect with our incredible fans across Europe. Their support will be vital as we build momentum."