There's another problem with the way the Maguire "transfer" is being presented and that is the Premier League wages cap.
These are laid out in the PL handbook in section E-19 that anyone can download from the PL web-site.
In brief, your wagebill can increase each season by £7m which is very approx £150k pw to keep it in simple figures. In the past Utd have circumvented this rule as you can use rising revenues to offset excess....but Utd are out of the CL so this this season they have to adhere to the rule.
In the Summer, Utd released Herrera and Valencia. I don't know how much they were on, but given that Utd have the highest wage bill in the country let's assume that it's £400k pw between them. That means that they have £550k pw to play with but they've already used £200k on James and AWB, so it means that they have £350k pw headroom.
The result is that they are juggling players wages. They could just about meet Maguire's wage-bill, but it would be close, and I don't think they would want to be right on the edge as it would allow them zero flexibility in the event of injury etc in the Jan window.
Of course you wont see this mentioned in the papers because they use transfer headlines to sell papers, but Maguire can only really become a Man Utd target if they sell another player i.e. Lukaku. This is another reason why James and AWB were targets for Man Utd.....low wage expectations (only £100k pw - they are low compared to Pogba and Sanchez).