Crystal Palace have rejected a bid rising to £50m for right-back Aaron Wan-Bissaka, according to reports coming out of England.
United are said to have proposed an initial £35m upfront, with additional payments totalling to £15m.
The Eagles are understood not to be happy with the structure of the proposed deal, for the England U21 international who broke to the scene last season.
But it is believed they would accept an offer of between £45m and £50m up front.
Wan-Bissaka is understood to be considering a switch to Old Trafford, but he has yet to formally make his intention known.
Palace are under no pressure to sell the 21-year-old, who featured 39 times in all competitions last season as the Eagles finished in 12th place.
United manager Ole Gunnar Solskjaer is keen to bring in a right-back this summer following the departure of club captain Antonio Valencia.
The Old Trafford club will be hoping Wan-Bissaka put some pressure on Palace by agitating for a move.