De Gea has agreed terms on a deal with Real worth over £3.6million a year

David de Gea's Manchester United future is in serious doubt — with Louis van Gaal revealing he has lined up replacements and reports in Spain claiming the goalkeeper has agreed to move to Real Madrid.

The United manager has warned the 24-year-old, who is stalling over a new contract, that he has identified players to step in should he move to the La Liga giants.

And with reports in Spain stating that De Gea has agreed terms on a deal with Real worth over £3.6million a year, the writing would appear to be on the wall.

Manchester United goalkeeper David de Gea (right) looks set for a summer move to Real Madrid

 Marca claim an agreement betweeen De Gea and Real Madrid was reached months ago

United boss Louis van Gaal may have to begin searching for a replacement goalkeeper at Old Trafford

Spanish newspaper Marca claim an agreement was reached months ago and say only United's insistence on being paid £29m for the Madrid-born star, who is out of contract next season, is holding up the move.

'We want him to sign but he has to want to stay here at Manchester United,' Van Gaal said ahead of Sunday's visit of Arsenal. 'I don't know why he has not made the decision.'

Indeed, Kane's commercial worth to the club was underlined yesterday as he featured in the club's promotional material for the launch of their new kit.

Van Gaal has also been linked with Real's out-of-form Welsh winger Gareth Bale, who could be used in an exchange deal for De Gea. But he would not be moved on his targets.

'I see that I buy everyone in the world but it is not like that,' he said.

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Tottenham have told United that 30-goal striker Harry Kane is not for sale this summer 

United, in fourth place, will be without Wayne Rooney (dead leg), Luke Shaw (facial injury), Michael Carrick (calf) and Rafael (rib), while Jonny Evans is an injury doubt for the visit of the third-placed Gunners.

On Thursday executive vice- chairman Ed Woodward said he was 'delighted' with Van Gaal's performance after the club all but secured their target of Champions League football for next season.

'It's not bad I think,' Van Gaal agreed.