Manchester United led twice in Wroclaw before Milan turned the game around in the closing minutes, with Harry Maguire and Patrick Dorgu scoring for United, and Samuel Chukwueze, Alfadio Cissé, Gonçalo Ramos and Ruben Loftus-Cheek finding the net for Amorim's side.
Amorim, now in charge at Milan, sought out several of his former players after the final whistle, with most of the United squad walking over to greet him and shake his hand. Footage showed Marcus Rashford, Kobbie Mainoo and Diogo Dalot keeping their distance instead, with none of the trio approaching or embracing the Portuguese coach.
Rashford's fallout with Amorim is the most striking of the three. The forward fell outside the manager's plans and spent last season away from Old Trafford on two separate loan spells, first at Aston Villa and then at Barcelona.
Mainoo also struggled for regular game time under Amorim, who was sacked by Manchester United in January after a run of poor results saw the club fall out of the title race.
Dalot's snub was harder to explain, with no known public conflict between the pair. Amorim had openly criticised the Portuguese defender's level at times, though Dalot later praised his former coach and stressed that the demanding standards had raised performance levels across the whole squad.
By contrast, several other former Amorim players were quick to greet him warmly, with captain Bruno Fernandes among the first to approach his compatriot, followed by Noussair Mazraoui, Luke Shaw, Joshua Zirkzee, Ayden Heaven, Lisandro Martinez and Matheus Cunha.
The contrast between the warm reception from most of the squad and the cold shoulder from Rashford, Mainoo and Dalot underlined how divisive Amorim's 14-month spell in charge at Old Trafford proved to be, before Michael Carrick took over on an interim basis.