Louis van Gaal on Wednesday warned his raft of new signings they would have to fight for their Manchester United places as the Premier League giants prepared to kick-off their pre-season tour of the United States.

United arrived in Seattle in buoyant mood after bolstering their squad with a slew of high-calibre new arrivals led by Bayern Munich midfielder Bastian Schweinsteiger and France international Morgan Schneiderlin.

With highly rated Dutch international Memphis Depay and Italy defender Matteo Darmian also joining in the close season, van Gaal is confident he can build a team to re-establish United as title challengers.

But the veteran Dutchman warned that all of the new signings would need to prove they deserved a place in United's starting line-up.

"I have to say to the players, you have to fight for your position," van Gaal said.

"Never is it secure in top sport -- even my position is not secure.

"But also the players, the players have to fight. Morgan Schneiderlin has to fight with Schweinsteiger, Michael Carrick, Daley Blind -- these are the players who can play in the centre of midfield.

"Matteo Darmian has to fight with (Antonio) Valencia, he knows that but Valencia knows that also."

Darmian, who joined from Torino, would help to shore up United's defence while also providing an attacking threat, van Gaal said.

"He has a very good orientation and with that he can cooperate with our central defenders," van Gaal said.

"He is fast. He is also a reasonable header so that is also a plus. He can build up and he can see a free man and he is in an attacking way a good player."

Van Gaal meanwhile praised United chief executive Ed Woodward for helping get the bulk of the club's transfer business done before the pre-season.

Woodward faced stinging criticism for his performance in the transfer market in 2013 after missing out on a number of high-profile targets including Spaniards Thiago Alcantara and Cesc Fabregas.

But van Gaal praised the United executive on Wednesday.

"To get these players, it is not so easy," he said.

"I am very proud, especially Ed Woodward, has done that.

"It is not so easy when Manchester United is coming -- they (clubs) are always asking more money than you think you should spend. They are here at the right time."

United begin their International Champions Cup campaign against Club America of Mexico on Friday at Seattle's CenturyLink Field.
Source: AFP