Manchester United face a serious battle to convince David de Gea to stay at Old Trafford beyond the end of his current contract.

United are invoking an option to extend the Spain goalkeeper’s existing deal by 12 months until the end of next season.

But talks over a new long-term contract have reached an impasse and United are now under growing threat of losing De Gea for nothing in June 2020, or being forced to cash in before then on their No 1, another unwelcome concern for a club in the throes of crisis.

United still have time to try to persuade De Gea that his long-term future will be best served at the club.

But the goalkeeper, who turns 28 next month, wants to be competing for the top domestic and European honours and United’s severe struggles have raised doubts about the team’s ability to challenge on both fronts.

With the future of manager Jose Mourinho also up in the air, De Gea is reluctant to commit what are likely to be his peak years to United at a time when there is so much uncertainty on and off the pitch.

De Gea won the FA Cup under manager Louis van Gaal in his first season after his proposed move to Real Madrid fell through after the deal fell through on deadline day credit: Getty Images

Mourinho has lost the support of much of his squad, but even if a new manager was installed at Old Trafford, it is likely De Gea would need to see a huge uplift in United’s competitiveness for his current thinking to change.

United came from two goals down to beat Newcastle 3-2 on Saturday but they are seven points adrift of the top three after eight league matches and already five behind Arsenal in fourth. They play Chelsea at Stamford Bridge after the international break.

De Gea was signed by Sir Alex Ferguson from Atlético Madrid in 2011 but it is now five-and-a-half years since the goalkeeper won his one and only Premier League title with United. The club have lifted the FA Cup, League Cup and Europa League since then but it has not been enough to satisfy De Gea’s ambitions.

United officials met with De Gea’s agent, Jorge Mendes, in London on Friday but they have been unable to come to an agreement over a new contract and the club will now have their work cut out trying to retain their most outstanding player beyond the short-term. De Gea has been named United’s player of the year in four of the past five seasons.

The Spaniard came close to joining Real Madrid in September 2015 when Louis van Gaal was manager, only for the deal to collapse on transfer deadline day. De Gea then had another opportunity to join Real in the summer of last year only for the Madrid club to back out of a move after Mourinho had paved the way for the goalkeeper to go.

Mourinho said Real’s decision left an ill-feeling with De Gea, and the Madrid club subsequently signed Thibaut Courtois from Chelsea this summer, but there are unlikely to be a shortage of takers for arguably the world’s best goalkeeper the longer his contract at United runs down.

De Gea was heavily criticised for his performances for Spain at the World Cup finals in Russia over the summer but he has been in impressive form for United again this term.

De Gea is playing in front of an ever changing back line and United’s defensive woes this season have underlined why Mourinho was so keen to recruit a centre half in the summer only for moves for Harry Maguire and Toby Alderweireld to be vetoed by the club’s hierarchy.

Mourinho - who has deployed midfielders Ander Herrera, Scott McTominay and Nemanja Matic in central defence this season - remains in the market for a defender in January and, in a bizarre twist, veteran Sweden centre half Andreas Granqvist has claimed there is interest in him from United.

The 33-year-old, formerly of Wigan Athletic, plays for Helsingborgs and captained Sweden at the World Cup, where they lost in the quarter-finals to England. "There certainly is interest,” he told Swedish newspaper Expressen. “I’m flattered even to be mentioned with such a big team as Manchester United.

“Should there be a concrete offer in January, I'll receive it and then Helsingborg will look at it. I don't know if it's a loan. As I've not had a concrete offer, it's hard to speculate.”