Last updated on .From the section Football

Louis van Gaal and Robin van Persie

Manchester United's players could be in for a tough time following Louis van Gaal's appointment, says ex-Netherlands midfielder Ronald de Boer.

"He's very strict," De Boer, who played under Van Gaal for club and country, told BBC Radio 5 live.

"When I was young, I was scared of him and feared him a bit."

Manchester United: Van Gaal is new manager

United finished seventh in the Premier League and failed to qualify for Europe for the first time in 25 years, leading to the sacking of David Moyes.

Van Gaal, who has won titles with Ajax, Barcelona, Bayern Munich and AZ Alkmaar, will take charge at Old Trafford after leading the Netherlands at this summer's World Cup in Brazil.

The 62-year-old Dutchman has signed a three-year contract.

Former Rangers forward De Boer, who played under Van Gaal at Ajax and Barcelona, believes United's new manager will quickly get the best out of the players.

"Everyone knows which direction he is aiming for and everyone will follow that," said De Boer, who is youth team coach at Ajax.

"When he watches, you give a little more effort in what you are doing."

Derby manager Steve McClaren, who led Dutch side FC Twente to the Eredivisie title and was assistant to Sir Alex Ferguson at Old Trafford, agrees that Van Gaal is a tough taskmaster.

"He is very forthright, he knows what he wants, he knows what he is doing and he is very disciplined," McClaren said.

Glory for Van Gaal National titles: Ajax (1993-94, 1994-95, 1995-96), Barcelona (1997-98, 1998-99), AZ Alkmaar (2008-09), Bayern Munich (2009-10)

Champions League: Ajax (1994-95)

Uefa Cup: Ajax (1991-92)

"You either love him or you hate him in Holland, he is one of those characters, but he is successful, he gets teams winning and he is experienced at that level."

Known for employing an attacking style and his demands for discipline from his players, Van Gaal came to prominence when he guided a young Ajax team, featuring Clarence Seedorf, Edgar Davids and Patrick Kluivert, to a Champions League final victory over AC Milan in 1995.

He won two Spanish league titles with Barcelona, led AZ Alkmaar to only the second Dutch title in their history, and then, in his first season in charge, took Bayern Munich to the German title and the Champions League final in 2010.

He has a strong relationship with United striker Robin van Persie, appointing the former Arsenal player Netherlands captain in June 2013, and is expected to be given significant transfer funds to bring in new players at Old Trafford.