With United trailing 2-1 to Arsenal in the FA Cup quarter-final, Di Maria was booked for diving and minutes later grabbed the shirt of referee Michael Oliver, giving the shocked official little choice but to send him off.
It ended United's hopes of hauling themselves back into the tie and marred what had started off as a bright performance by the man signed from Real Madrid for 60 million pounds ($90.65 million).
Van Gaal, who now has virtually no chance of marking his first season with a trophy, had little sympathy for Di Maria.
"In Spain he knows that he doesn't touch the referee, but that is also in his emotion," the Dutchman told the BBC.
"I've already spoken with him, he knows my opinion but also I have to see on the video.
"I think he's touched the referee and that's forbidden in every country, so he has no excuses."
When Wayne Rooney cancelled out Nacho Monreal's opener for the visitors before halftime with a flying header, United looked as though they might continue their quest for a first FA Cup since winning a joint record 11th in 2004.
But they faded after the break and now only have a desperate battle for a top-four Premier League finish to play for.
That it was Danny Welbeck, sold by Van Gaal last summer, who poached the winner after a dreadful mistake by Antonio Valencia only rubbed salt into the wound.
"We didn't lose to them, we lost because of our own performance, and that's very disappointing," Van Gaal said.
"The players are very disappointed, they know it could have been different. It's a pity because after we were 1-0 down, we recovered immediately.
"We gave the ball away in an area where you cannot give the ball away and that's very disappointing," he added.
"I think the best man in my team made the error and it was decisive. These things happen."
(Reporting by Martyn Herman; Editing by Peter Rutherford)
Share
