David de Gea's agent Jorge Mendes has hinted that the Spaniard may make a move to Real Madrid in the future, putting a question mark over his long term future at Manchester United.

The stopper, who is set to replace Iker Casillas in the Spain national team has also been tipped to take over from the veteran at Madrid, fuelling rumours over a possible move in the summer.

De Gea's deal with United expires in 2016 with United reportedly valuing the player at around £50m and hoping to use him in a swap deal for Real Madrid midfielder Gareth Bale.

De Gea has been United's standout performer this season, saving them innumerable points, when the Red Devils struggled to strike a chord in the Premier League in attack and defence.

Louis van Gaal's tactics have not always made sense, leaving De Gea to make a multitude of saves to take three points at Arsenal, Everton and others.

His form has attracted interest from Madrid and with contract negotiations still in the works there is panic in the United contingent. Mendes' recent comments over the Spaniard's future have not helped matters either.

"David is amazing, he's brilliant. He's a Man United player and has a contract there. You have to respect that but things change every five minutes," Mendes said.

United are aware of the interest and have already made contingency plans in the form of former Barcelona stopper Victor Valdes, who signed for a free in January. However, Van Gaal has not given up on De Gea signing a new contract, stating in an interview recently that the player will commit his future to United.

"I think so, yes. I think there is no problem for him to sign. It's the same as other players. You can ask other players and I can answer the same," Van Gaal explained.