The former Real Madrid player joined United for a British record £59.7 million last season, but after an impressive start at Old Trafford, with three goals in his first four games, he suffered a two-month injury layoff and failed to score again in the league.
Towards the end of the season he was regularly left out by Van Gaal and was sold to French champions Paris St Germain for a reported €63 million after the campaign.
“It is difficult to adapt to Van Gaal because he points to his philosophy,” the British media quoted Di Maria as telling ESPN Radio in Argentina, where he is currently on international duty preparing for the game against Bolivia on Saturday.
“Everyone takes what he wants and does. I started very well with him and then had a couple of clashes.
“There came a time when I did not have a good relationship with Van Gaal and that influences much in a player’s mind,” the 27-year-old Argentina winger added.
“At Manchester United I played very well but then got injured. Things did not work out and I also changed my position.
“The coach was the one who decided that and I ended up being more on the bench than in the team.”