When an agreement between the clubs was first announced on 5 October 2020 - deadline day at the end of the summer transfer window - it was subject to a medical, work-permit and personal terms.
These steps in the process have been completed, and an application has been made for a visa. Once this has been issued, Diallo will be cleared to travel to Manchester and to train with and play for Ole Gunnar Solskjaer's side.
Diallo featured twice for Atalanta's first team earlier this season, both as a substitute in home games. He played the last 10 minutes against Hellas Verona in Serie A on 28 November, and then faced FC Midtyjlland a few days later in the Champions League, coming on in the 68th minute.