The Portuguese boss has been keen to keep hold of his star man but knows Real Madrid are determined to sign him this summer.
Real Madrid chief Florentino Perez has been keen to bring him to the Spanish capital for some time and came close to signing him in the summer of 2015.
He remains hopeful of securing his signature this time around but Mourinho is playing hardball.
It seems Mourinho has now delivered the La Liga champions a message over De Gea’s sale following talks with his former club.
And the 54-year-old wants to ensure he gets more than his fair share out of the deal.
The Daily Star claim Mourinho has told Madrid he will sell De Gea if Madrid fork out £45m AND give them Alvaro Morata.
A Manchester United insider told the paper: “De Gea – as long as Real pay £45m and Morata.”
The Spanish striker has been edging closer to a move to Old Trafford although a fee is still proving difficult to agree between both clubs.
Madrid value Morata themselves at around £60m but United have so far been reluctant to meet their asking price.
But the Red Devils hope to take advantage of Madrid’s desperate attempts to finally sign De Gea by getting the talented striker.
Mourinho is on the lookout for a new striker with Zlatan Ibrahimovic leaving the club and Wayne Rooney’s future uncertain.
And with Everton’s Romelu Lukaku looking likely to pick a return to Chelsea over United, Morata remains his priority target.
Should Madrid pursue De Gea, Mourinho will be left to find a new shot-stopper – although he remains a big fan of backup Sergio Romero.
The Argentine shot-stopper inspired United to Europa League glory last term and Mourinho could take a chance on making him his first choice next term.