The Red Devils were already on the hunt for a left-sided defender before the arrival of new boss Ruben Amorim.
Dimarco, who is 27, was seen as someone who could be a regular in United's first team.
However, he is said to be very happy at Inter, where he has won the Serie A trophy.
According to Tuttosport, he has told all suitors that he is very satisfied with his current situation.
Inter also rejected United's proposal, because they want to keep the defender.