The 25-year-old goalkeeper, who has been in top form this season, has been time and again linked with a big-money move to Real Madrid, despite United stubbornly insisting that De Gea is not for sale.
The Spaniard, who has 18 months remaining on his current contract at Old Trafford, also claims that he is happy at United, but the Red Devils are reportedly afraid that the goalkeeper may change his mind if he gets a lucrative offer from the Spanish giants.
Due to this reason, United have reportedly put a £50 million price, and are looking to tie down De Gea on a new five-year deal worth £200,000-a-week, according to the Daily Express.
Although Real Madrid, who have reportedly identified De Gea as a long-term replacement for Iker Casillas, are more than capable of matching United's £50 million valuation for the Spaniard, it is unlikely that they will spend so much money on a goalkeeper.
Earlier there were reports of Manchester United wanting to strike a player-plus-cash deal involving De Gea with Real Madrid for their winger Garth Bale, but the club recently played down these suggestions, insisting that manager Louis van Gaal is more interested in keeping the Spanish goalkeeper at Old Trafford.
United fans have also made their feelings clear as a recent survey conducted by MUST (Manchester United Supporters Trust) revealed that 99 percent of supporters would prefer to see De Gea stay rather than Gareth Bale come to Old Trafford.
"With this in mind it signals the challenge Ed Woodward [United's executive vice-chairman] and the Glazers have to get United's most popular player signed up on a new contract, before Real Madrid attempt to prise him away," a MUST spokesperson told the Daily Express.
De Gea, who arrived at Old Trafford from Atletico Madrid for £18.6 million (the British record fee for a goalkeeper), has managed to establish himself as one of the best goalkeepers in the Premier League after initially struggling at Old Trafford.