Jose Mourinho is desperate to splash the cash before todayâ€™s 5pm deadline.
The Red Devils have completed three deals, with Fred, Diogo Dalot and Lee Grant heading to Old Trafford.
However, Mourinho wants at least two more signings today, with a centre-back his top priority.
Leicesterâ€™s Maguire, Tottenham star Alderweireld and Boateng of Bayern Munich are targets for the Red Devils.
And according to Sky Sports, the Old Trafford board would rather sign Englandâ€™s World Cup hero Maguire out of the trio.
However, they say Mourinhoâ€™s preferred choice is Germany international Boateng.
Leicester are demanding around ÂŁ75m for Maguire, who impressed at the World Cup in Russia this summer.
However, the Foxesâ€™ stance hasnâ€™t changed, with Claude Puel currently refusing to sell the former Hull star before todayâ€™s deadline.
Should Bayern defender Boateng head to Old Trafford, it would likely be a loan deal.
As for Alderweireld, Spurs are said to be keen to sell the Belgium international, providing United meet their valuation.
Mourinho cut a frustrated figure during Unitedâ€™s pre-season tour of America.
The Red Devils boss has been vocal on his summer transfer plans, revealing heâ€™s far from happy with the Old Trafford board.
â€śWe basically have the same players,â€ť said Mourinho.
â€śThe players we have bought, one is a goalkeeper cover, one is a 19-year-old kid, so in fact we have one new player which is Fred.
â€śSo of course our team is not going to be very different.â€ť
Mourinho is desperate to splash the cash to catch Manchester City this season.
United watched on last time out as Pep Guardiolaâ€™s side stormed to the Premier League title, with City breaking the 100-point barrier for the first time.
Man Utd transfer news – who has Jose Mourinho signed this summer?
Players in:Â Fred (ÂŁ47m, Shakhtar Donetsk), Diogo Dalot (ÂŁ19m, Porto), Lee Grant (ÂŁ1.5m, Stoke).
Players out:Â Dean Henderson (loan, Sheffield United), Joe Riley (undisclosed, Bradford), Sam Johnstone (ÂŁ6.5m, West Brom), Daley Blind (ÂŁ14.1m, Ajax), Matty Willock (loan, St Mirren), Cameron Borthwick-Jackson (loan, Scunthorpe), Max Johnstone, Jake Kenyon, Ilias Moutha-Sebtaoui, Devonte Redmond, Theo Richardson, Charlie Scott (all released), Michael Carrick (retired).