Speculation linking the 23-year-old with a move away from the King Power Stadium refuses to go away as he continues to shine for the Foxes and it may not be long before United make their move.
Reds boss Ole Gunnar Solskjaer is said to be finalising his list of transfer targets and it is no surprise that Maddison is on it as he ticks all of the boxes for the Norwegian.
He is the right age, has the right attitude and has shown what he can do this season with four goals and four assists as Leicester have jumped to second in the Premier League table.
The Foxes will point blank refuse to sell in the January transfer window as they look to cement their place in the top-four and reports claim they are also working to get Maddison tied down to a new contract.
The former Norwich City star is under contract until the summer of 2023 so Leicester are in a strong position.
However they hope by offering him a fresh deal on much-improved terms, it could convince him to ignore United's advances.
That may be wishful thinking however as it will be difficult to ignore a club like United even if they are struggling at the moment.
Maddison is said to be a boyhood United fan and is also close friends with Harry Maguire, who made the switch from Leicester to Old Trafford in the summer.
United finally landed their man then and will be hopeful of doing the same again if they keep chipping away at the Foxes and offer a big enough fee.
That could be in the region of £80million but will go even higher if Maddison carries on shining in the Premier League season and earns a place in the England squad for Euro 2020.