Maddison will be 23 by the time of the next transfer window, and the Manchester Evening News reports that United consider that to be the ideal age for any new recruits.
At 23 Maddison will have proven himself over two seasons in the Premier League, but be young enough to develop further should he arrive at Old Trafford.
United are aiming to add more players to the squad over the next two transfer windows, with Ole Gunnar Solskjaer retaining the support of the board despite a dreadful run of form. The club hope that the side will turn around their fortunes after a decent point against Liverpool, and a better performance than has been seen in months under the Norwegian.
United are encouraged by the fact that they successfully dealt with Leicester in the pursuit of Harry Maguire in the summer for a fee of £85 million, though United had to pay £80 million up front to secure his signature. There will also be pressure upon the club to complete any deal before the start of the Euro 2020 championships, because an impressive international showing could see his valuation dramatically increase.
The MEN believes that United could end up having to pay a similar amount for Maddison, and the club would be able to afford such a fee despite being locked out of the Champions League for at least the rest of this season.
The club expect Mario Mandzukic to arrive in January for a fee of around £10 million, with some papers reporting that he has dropped his wage demands of £300,000 a week, but that seems like a bit of a ridiculous claim to be honest.