Former Manchester United left-back Mikael Silvestre has defended the record-breaking signing of Luke Shaw, after the England international became the most expensive teenager in the world upon moving to Old Trafford.

Shaw joined United from Southampton last month to become the club's second signing of the summer for a fee in excess of £30m, which eclipsed Wayne Rooney as the world's most expensive player aged under 20.

But Silvestre, who played for United for nine years under Sir Alex Ferguson, says the length of Shaw's contract means the deal has long term value to manager Louis van Gaal.

"You have to look at the entire deal here," Silvestre told

"Okay, the sum is £30m but how long has he signed for? Four years. So you have to keep that in mind as well. I know it's expensive if you look at it this way but when you join Manchester United you don't stay there for just one year, you will probably be there for four or five years.

"I stayed there for nine years. So overall, after six or seven years, you won't say that it was an expensive deal. It is a good investment by the club."

Shaw joined Herrera as United's second summer addition, deals which are in stark contrast to the policy of former manager David Moyes who made his only significant signing of last summer on deadline day after luring Marouane Fellaini from Everton.

That haphazard summer set in motion a torrid spell for Moyes at United, where he lasted just eight months and failed to guide the club into the Champions League.

Van Gaal, a former European Cup winner and current coach of Netherlands who stand 90 minutes away from the World Cup final, was confirmed as his successor in May and Silvestre is confident the appointment will pay off.

"As soon as he was announced as the new manager, I was convinced that he will be a good one for United," he added.

"He has a great record for both club and country and he is just showing that in the World Cup with Netherlands. He has got what it takes to be a manager for a club like United and he is coming at the right time.

"There have already been two signings and we can expect more by the end of August, so we will see then. They lost two centre-backs this time and so we can expect the manager to sign a couple of experienced players in that area."