De Gea is yet to sign a new deal despite the club taking up the option of extending his deal for a further year until 2020.
However, he is understood to be holding out for a big pay-rise to extend it beyond that.
Previous reports claim he wants parity with Sanchez who earns a basic wage of around £350,000 per week with add-ons that could take it closer to £500,000.
But sources say executive vice-chairman Ed Woodward has told the goalkeeper’s agent that an increase of such magnitude will not be possible and that could be a huge worry for the club’s fans.
Paris Saint-Germain are reportedly willing to meet his demands to take him to France as they are desperate for a new keeper.
United might now need to cash in on him this summer or risk losing him for nothing at the end of next season.
Despite a difficult campaign by his own lofty standards, De Gea remains a key player for United and has won the club’s player of the year on four separate occasions.
It is also claimed that Ole Gunnar Solskjaer is so desperate to keep him that he has intervened in talks with De Gea growing increasingly frustrated at a lack of movement.
His efforts might be in vain, though, as the report says United are not willing to offer any more deals like the four-and-a-half year one Sanchez was given when he joined from Arsenal last January.
He has struggled since arriving at Old Trafford and could now be sold as United look to overhaul their squad.
Ander Herrera also looks set to leave on a free transfer at the end of the campaign with PSG his most likely destination.
Marcos Rojo will also be allowed to leave and Fenerbahce have been heavily linked with above for the Argentine defender.