Manchester United would regret selling Angel Di Maria, former Uruguay international Diego Forlan has said in The National.
Di Maria, 27, had a mixed debut season for United following his £59.7 million move from Real Madrid last summer.
The winger started impressively but struggled to shine in the second half of the campaign, scoring three goals in 27 Premier League appearances overall.
Forlan, who played for the Red Devils between 2002 and 2004, is sure the Argentina international is worth persisting with, as shown in his recent performances at the Copa America.
He said: "Di Maria looks happy and comfortable playing for his country, unlike when he plays for Manchester United in the Premier League.
"I thought he was a superb signing for United because he is one of the best players in the world, but I was slightly surprised, too. Louis van Gaal has never been a fan of South American players, as my good friend Juan Roman Riquelme will tell you from his time under the Dutchman at Barcelona.
"Van Gaal also had a habit of letting his South Americans leave when he was at Bayern Munich, yet United signed both Di Maria and Radamel Falcao, the Colombia striker, on huge money last summer.
"Di Maria started out in England like the player we knew he was at Real Madrid in the 2013-14 season. He looked a class above opponents, he ran at defenders, he was a danger around the box and he covered so much ground. Less talented players have felt they were too good to work as hard as him.
"But then it all went wrong. He lost his place in the team, he didn't look happy. It was the same for Falcao, who ended up leaving at the end of his loan deal this summer.
"Players are not robots and if there's something wrong then their coaches need to find out what the problem is. Di Maria is worth the effort. He offers something different from almost every other player.
"Real Madrid really missed his driving runs last season. He is quick, he makes assists and he can also do the hardest thing in football -- beat a player one-on-one.
"United will regret it if he leaves. He should be given another season to prove himself and United should try to understand him better and trust him.
"Great coaches and great players don't always get on and not every player fits into rigid systems, but Di Maria is worth persisting with."