Fletcher: United will click in time
United's new manager stretched his winless streak to four matches on Saturday with a 0-0 draw at Burnley.
Despite the introduction of record signing Angel di Maria, Van Gaal's team rarely looked like beating the Barclays Premier League newcomers.
Midfielder Fletcher admits it has been an immediate test to get to grips with the new 3-4-1-2 system implemented by Van Gaal, but the Scot is sure everything will click into place eventually.
"It's mentally challenging but that has always been the case," the United vice-captain said when asked about the difficulties of adapting to a new formation.
"The players are learning a new system and developing ideas. It is going to make us better players in the long term.
"These things take time and we just have to keep believing in the manager's philosophy and ideas.
"There are other things that come into it, it's not just the system, but I am confident we will put things right."
United have spent upwards of £130million on four new players this summer.
They are expected to complete a £13.8million deal for Ajax's Daley Blind before Monday's 11pm deadline and a number of departures are also expected.
Fletcher believes the United boss has every right to make big changes given the club's seventh-place finish last term, and their performances so far this year.
"The manager was very straight and forward with the players and I think the players appreciated that," Fletcher said.
"You expect that after a disappointing season like last season."
The only plus point from the game at Turf Moor, other than the fact the team kept a clean sheet, was the performance of Di Maria.
The Argentinian, who only landed in Manchester on Tuesday, stretched Burnley's back four with his pace and he also created a number of chances with some exquisite passes.
Fletcher thinks the Â£59.7million man will prove to be a top player for the club.
"I expect him to be a great player for United," the United midfielder said.
"He is a fantastic player. He showed glimpses of what he has got.
"He is very powerful, dynamic, has an eye for a pass, and has an eye for goal.
"I thought he coped well with everything at Burnley, it's not an easy introduction.
"He has given everyone a lift. It's fantastic to have players like that and he will only improve us."
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