Louis van Gaal has admitted it will not be easy to sign the new players he thinks are needed to improve Manchester United.

The Red Devils flew home yesterday after completing a near-perfect pre-season tour of the United States.

Despite only taking up his position just two days before leaving for the USA, Van Gaal racked up victories over the Los Angeles Galaxy, Roma, Inter Milan, Real Madrid and Liverpool.

Almost everything went to plan, but the Old Trafford boss is still not totally content with his squad.

The Dutchman has admitted he wants to sign new defenders before the season starts, but he concedes landing his targets will prove hard.

"Manchester United shall buy players when we can improve our selection," said van Gaal.

"And that is a lot more difficult than you think."

Arsenal's Thomas Vermaelen and Borussia Dortmund centre-back Mats Hummels remain van Gaal's top targets - but signing the latter is proving hard because the German club have already lost one star in Robert Lewandowski, who joined bitter rivals Bayern Munich this summer.

Another priority for Van Gaal is cutting loose the players he deems surplus to requirements.

Those who are surely in the most danger include Javier Hernandez, Nani, Shinji Kagawa, Marouane Fellaini and Anderson.

Van Gaal will not enjoy telling his unwanted players they have no future at the club, but he will not shirk away from making the changes he feels are necessary either.

"I won't come with the axe - it's not like that," Van Gaal said.

"We have to be honest. We have to give advice to the players now at this moment and not at the end of August. Then we can't change anymore and they don't have a choice.

"Of course it's difficult to say something after two weeks but I think you have to say something."

England star Wayne Rooney thinks the new coach has made a big impact at Old Trafford.

Rooney said: "Since he has come in he has given us all a different way of looking at football. It's been great for us and hopefully that will continue."

United confirmed yesterday that a deal had been finalised with FK Vojvodina for the transfer of 17-year-old goalkeeper Vanja Milinkovic.

The 6ft 7in stopper will spend the coming season on loan at the Serbian club before moving to Old Trafford next summer.