Louis van Gaal says the fact that the summer transfer window remains open once the season is under way is “ridiculous” and that he had tried to get the dates changed on many occasions.

Van Gaal has already signed Memphis Depay from PSV Eindhoven but believes the window’s closing date of 1 September, three weeks into the new season, should be moved.

Asked if this close season could be one of the trickiest of his career, Van Gaal said: “You can never say that in advance, because what I have said is it’s a process. It’s not so easy, because when you sell a player there are also three parties. The same when you buy a player and you never know which party is struggling or not struggling. It’s also ending on 31 August or 1 September and that’s ridiculous in my opinion.

“I have strived many times to change the transfer period. It has to be finished before you prepare your team for the season. Last summer we had the World Cup and then a lot of players came late in. We had a lot of purchase at the last month so we have to prepare our team in the Premier League and that costs us a lot of points. Now I hope we shall finish our business much earlier.”

Van Gaal admitted Robin van Persie’s future at the club is in the balance, as reported by the Guardian earlier this month. The manager would not confirm whether the striker will be at United next year. “You have to wait and see. I shall not say who I am speaking to [about the future].”

Van Gaal is unclear how many new players he requires to ensure the balance of his squad is correct. “I think that is also dependable on how many players shall go. That’s also an issue. It’s a process and not a matter of one or two players. I cannot say anything about that,” he said.