Paul Pogba's talent has been in evidence for years- that was why the Reds signed him from Le Havre in 2009 when he had already captained France's Under 16 team.
Now 23, he has a tendency to drift in and out of matches - he was not a consistent perfomer at Euro 2016 and did not appear to relish the deeper role given to him by coach Didier Deschamps when France lost to Portugal in the final.
Pogba is not the finished article but the promise United first identified seven years ago is showing signs of being fulfilled, more than enough to persuade the club to potentially pay such a massive fee.
It is tempting to say that if a club spend going on £100 million on a single player, the system fits around him, not the other way round, but modern football does not usually work like that.
Even the best players can struggle without a structure or if they are played out of position.
It is still a source of bewilderment to staff at United as to why Angel Di Maria was so chronically alienated by former manager Van Gaal.
The previous record signing at £59.7 million was used as a holding midfielder or wing-back by the bizarre Dutchman having begun his Old Trafford career with three goals and three assists from his favoured offensive position.
Pogba is a rarity in the modern game in that he is capable of both attack and defence, he is quick, has energy and can tackle.
Though not a prolific scorer, his average of one goal every five games suggests he will be an attacking threat.
In short, he is the kind of player United have lacked since Roy Keane left in 2005 but without the fiery temper.
Mourinho will surely put him in the centre of his midfield and set his side up from there.
Wayne Rooney, for all his attributes, is no speed merchant.
Anthony Martial, Marcus Rashford, Jesse Lingard and Memphis Depay definitely are, making them better suited to wide positions.
If the plan is to play Henrikh Mkhitaryan wide, or deeper in midfield, there is an obvious place in the side for Rooney at number 10.
But is that going to get the best out of the talented Armenian? Mourinho likes his central midfield to contain aggressive, athletic players such as Claude Makelele and Michael Essien in his first stint at Chelsea.
Pogba is in that mould.
Morgan Schneiderlin and Daley Blind could work effectively alongside him.
If that happens, the uncertainty over Rooney will persist.
That the questions and doubts are so numerous come as a result of both our fifth-placed finish and the often awful performances that contributed to it.
Until they wake from the post-Ferguson slumber, the minutely forensic analysis of United and our players will go on.