The Premier League giants paid a hefty fee of €25m and another €15m add-ons were promised to Serie A side Atalanta before they signed the 18-year-old winger this month.
The deal was in place in the last summer and Manchester United obtained the work permit they needed to complete the deal for Diallo in the ongoing window.
The teenage winger has been expected to be gradually introduced to English football through the Under-23s, but it seems that could change.
Diallo trained with the Manchester United first-team squad on Thursday, where he is being closely followed by Ole Gunnar Solskjaer and his backroom staff.
It has been claimed the Manchester United manager is assessing whether he could throw Diallo into the mix against Liverpool on Sunday.
Manchester United are going to Anfield with a three-point lead at the top of the Premier League table.
Diallo could be unlikely to start against the Reds, but Solskjaer may be considering having him in the squad for their trip to Merseyside this weekend.
It remains to be seen whether the Manchester United manager decides to spring a surprise by including him in his plans for the big game at Anfield.