The concern is straightforward. Tielemans comes off a heavy run of matches and, reports suggest, dealt with a physical problem during Belgium’s World Cup campaign.
This is the kind of issue that can shape selection as much as form. A player can be fit enough to play, but not yet ready for the repeated demands of a new system and a new tempo.
The second issue is role. Tielemans appears to want more freedom in midfield, with reports suggesting he sees this move as a chance to play with fewer restrictions than he had at Aston Villa.
That sounds attractive, but freedom in midfield is never free.
That is why this is less about his résumé and more about fit. Tielemans can improve the passing quality of the side, but only if the structure around him holds.
His exit from Aston Villa also frames expectations. He is no longer arriving as a prospect. He is arriving as a player expected to settle quickly, lead phases of possession and lift the tempo of United’s midfield from the start.
The next storyline is obvious: whether Carrick trusts him immediately against Hull City, or eases him in while solving both the fitness question and the role that could define United’s early season.