A first-half penalty from Daniel Sturridge was followed by a decisive second from Roberto Firmino 17 minutes from time but the 2-0 scoreline would have been much worse had it not been for the heroics of goalkeeper David de Gea who made four or five decent saves.
A Europa League exit to their arch-rivals next week would put Van Gaal under even greater scrutiny, even with his side just three points off fourth place in the Premier League and still in the FA Cup.
To avoid that he needs to devise a game plan to counter Liverpool's high-tempo pressing style which did for them at Anfield.
"We did not cope with the high pressure of Liverpool. The pressure is not from the crowd," said the Dutchman.
"We had expected that and for me it was a surprise we did not cope with it because they did it at their home match this year.
"That raised the atmosphere in the stadium and they created big chances but we had a very good goalkeeper and because of that we were in the match."
Source: PA