Martial’s agent revealed earlier this month that the Frenchman was looking to move away from Old Trafford, as he has seen his playing time diminish since the arrival of Alexis Sanchez from Arsenal in January.
The Red Devils appear reluctant to sell Martial on the cheap though, with the Manchester Evening News reporting that the club have quoted ‘silly prices’ for the 22-year-old.
Martial signed for United in 2015 in a move worth an initial £36m. That figure rose to £44.4m after he scored his 25th goal for the club against Burnley, and several incentives will see Monaco earn a total of £56m for the player.
United’s response could be seen as expected as Spurs knocked back an approach by United to sign defender Toby Alderweireld in May. The Red Devils had hoped to conclude a deal for around £55m, although notoriously tough negotiator and Spurs chairman Daniel Levy held out for a higher figure.
Martial has just one year left on his current deal and with Manchester United keeping tabs on the future of Real Madrid superstar Gareth Bale, Mourinho may not stand in the way of Martial leaving the club.
Earlier this month Martial’s agent Phillipe Lamboley said:
"After thinking about all the possibilities, Anthony wants to leave Manchester United. When Manchester United, which is the most powerful club in the world, does not find an agreement in eight months of negotiations, it is that it does not really want to make him an important player."
"It is a well-considered decision. He is under contract, United will have the last word and we will respect the decision of the club, it will go to the end of its commitment.
"We do not have the same vision on Anthony's future. Without the unconditional support of the fans, Anthony would have already asked to leave United.
"I will not comment on the consequences of the January transfer window. Everyone will have his opinion, I think he must resume the course of his career. The time has come."