The 27-year-old has been unable to replicate the form that earned him a £59.7m move to Old Trafford during the July-August transfer window, but Van Gaal feels the Argentina international is not the only new acquisition struggling to adapt to life in Manchester.
The Dutchman pointed to his previous experiences in other European leagues, saying that it was normal for new signings to take up to a year to adapt to their new surroundings.
When asked how long he thought it would take Di Maria to settle, Van Gaal said: “The general answer is one year, but you can’t give a general answer.
“It is easy to say that, I cannot prove that. It is not scientifically proven.”
He added: “I think it counts for all the players that we have bought, the first season is always difficult. I have explained that in the press conference after the match (against Sunderland).
“For me it is not a big surprise, it is more a big surprise when he (Di Maria) adapted as quickly as possible.
“In Holland, Spain and Germany I had the same experience with players. We have to give him time, not just Di Maria but all the players. We wait and see.
“You can see it for every player we have bought, (Luke) Shaw, (Daley) Blind, (Ander) Herrera, (Radamel) Falcao and also Di Maria.
“It is dependable, you have to manage so many aspects. Not just the game, but the culture.”