Manchester United are bracing themselves for another battle to keep De Gea, with Real Madrid desperate to bring the 27-year-old to the Spanish capital.
Los Blancos failed to sign him three years ago and, though Keylor Navas has helped them win consecutive Champions League titles, they remain keen to snap up De Gea.
Their cause is helped by the fact the former Atletico star’s contract expires in 2019 and, as of yet, no renewal has been signed.
But Spanish website Diario Gol say Mourinho has instructed Manchester United to only sell De Gea if he is able to land Bale in return.
Bale’s own future is shrouded in uncertainty.
The Wales international has struggled for fitness during his four years in the capital and, as a result, the club could cut him loose at the end of the season.
United want him to spearhead Mourinho’s attack for next season.
The 54-year-old, despite poaching Alexis Sanchez from Arsenal, views Bale as the final piece in his attacking jigsaw.
And Diario Gol say the player holds the key to De Gea’s long-term future.
The Spaniard recently admitted he was in no rush to negotiate a new deal at United.
But he did described the Red Devils as being a “very special” club.
“I don’t think it’s the time to start talking about the future, it’s not the time to be talking contracts,” he told Sky Sports.
“We have lots of games between now and the end of the season.
“It’s all about getting your head down, focusing, working hard, competing in training, keeping fit and picking up points.”