Manchester United legend Paul Scholes has branded Angel Di Maria the "biggest disappointment" of the campaign alongside Liverpool's Mario Balotelli but urges Louis van Gaal to keep him at Old Trafford as the club needed that type of player to "compete at the highest level in the Champions League".

The Premier League giants broke the bank in the summer of 2014 to secure the services of the Argentine international for around £59.7m ($91m) after he led Real Madrid to both Champions League and Copa del Rey victories while also appearing in Argentine colours at the World Cup final.

But the versatile winger has failed to replicate that blistering form at Old Trafford.

Even though the former Real Madrid star scored three goals in his first five appearances for the club he has since failed to add any more goals to his tally in the Premier League. His only other goal came in the FA Cup victory over Yeovil Town.

Scholes admits he may have been the "biggest disappointment" of the season alongside Liverpool's Mario Balotelli but believes United cannot "afford to lose him" if they have title ambitions next season.

"A good start but, for £59.7m, the hope was that he would give United much more. I accept he has had problems off the pitch settling into life in Manchester, but there is no way he can see the season as anything other than a disappointment," Scholes wrote in his weekly column for Standard Sport.

"This was, after all, the best player in last season's Champions League final. Nevertheless, the quality is there and I don't think United can afford to lose him. They need that kind of player if they are to compete at the highest level in the Champions League. Let's see what next season brings."

Meanwhile, the United legend has named Tottenham's Harry Kane as the best breakthrough player of the campaign while comparing him with Ruud van Nistelrooy.

"It has to be Kane for forcing his way into the Tottenham team, staying there and scoring so many goals along the way. There was a goal against West Bromwich Albion, his first of two, on 31 January, which reminded me of Ruud van Nistelrooy at his best," he said.

"There was nothing gentle about it – quick feet and then a shot that was smashed past the goalkeeper. That was typical of Ruud. He was unwilling to give the goalkeeper any chance at all. You need that ruthlessness as a goalscorer.

"Kane's record of 31 goals in all competitions is superb, and his attitude is obviously excellent. I am sure that he knows next season will be difficult for him but there is no reason he cannot make progress again. I see him as a No 9, a classic centre-forward. I don't think he is a No 10 in the Teddy Sheringham mould. Sheringham would link the play but that is not Kane's game."