Iker Casillas-David De Gea
David De Gea is currently Iker Casillas's back up for the Spanish national teamGetty

Spain boss Vicente del Bosque has warned David de Gea it will be "very difficult" for him to retain his place in the national team squad if he remains frozen out of the Manchester United starting XI this season. The goalkeeper's role at Old Trafford is under scrutiny after his long-expected move to Real Madrid collapsed on Spanish transfer deadline day (31 August) as the necessary paperwork did not arrive at La Liga headquarters on time.

Louis van Gaal has left the Spaniard out of his squad for the first four matches of the Premier League campaign, saying the keeper was not mentally ready to play due to the transfer rumours. The Dutch gaffer did admit in August that, if De Gea stayed in Manchester beyond the end of the transfer window, he could still play again.

"Of course he could," Van Gaal said, as quoted by The Guardian. "If he is still here on 1 September we will look again, but he cannot play before that because as a goalkeeper you need the highest concentration, and it is difficult when you are in a position like David. We saw in pre-season his focus was not quite there."

United said in an official statement on 1 September that the club was delighted to have kept a "fan-favourite double Player of the Year" in the squad. However, it is uncertain whether Van Gaal will hand him the chance to regain his number one at Old Trafford ahead of current first-choice Sergio Romero, as he is out of contract next summer – and will be free to make the move to the Santiago Bernabeu at the end of the campaign.

Del Bosque has included De Gea in his 23-man squad for the forthcoming European Championship qualifiers against Slovakia on 5 September and Macedonia three days later, in the hope that the situation would have been resolved after transfer deadline day. But speaking with Cadena Cope following the collapse of the Real Madrid move, the national team manager warned De Gea that if he did not retain his first team spot at Manchester United, then he would not be in national team contention.

"I guess if he doesn't play it will be very difficult for him to come [to the Euros]," Del Bosque said. Asked whether he plans to have a private conversation with De Gea following the failure move to Real Madrid, he replied: "No, but if there is any need I will say something, but he will take this episode like any other. Everything that happens is for a reason. I want him to play and to be happy, and to play well so I can select him."