Manchester United: Retaining David de Gea will be club's biggest achievement says Phil Neville

Manchester United tying down David de Gea to a new long-term deal will be the Red Devils' biggest signing of the summer, according to former Old Trafford midfielder Phil Neville.

The Spanish goalkeeper, who will enter the final-year of his contract with the Old Trafford club, has been constantly linked with a move away from the 20-times English champions with Real Madrid being touted as his next destination.

De Gea has clearly been the best player for United this season, as he has singlehandedly kept them in games this season. According to a Daily Mail report, until midway through this season in December, the goalkeeper had earned United nine points on his own, without which they would have found themselves in the wrong half of the table.

Louis van Gaal is desperate to tie down the stopper to a new deal, as he is aware that the reigning European champions are looking for a long-term replacement for Iker Casillas, who is facing an uncertain future at Santiago Bernabeu.

Neville has urged the club to sort out his contract and believes that at no cost should the club let him leave, as the former Atletico Madrid star is currently at a stage in his career, where he has been labelled "world-class" by pundits and colleagues alike.

"The biggest thing is David De Gea, and keeping him at the football club," Neville said, as quoted by the Mirror.

"From when he first came, to how he is now, I don't think I've seen a player develop and improve as quickly as him. I saw with Cristiano [Ronaldo], I saw the development in terms of his performance, his size, his stature and his physique."

"He's now at the stage where you'd say he's world-class. He's winning football games on his own. It's a flippant thing to say but he really has," the former United mdidfielder explained.

"Last minutes saves against Everton, Hull, Arsenal away - there's seven or eight occasions where he has won United games which just shows you that he is world-class," he concluded.