Carroll scored a six-minute hat-trick against Arsenal at the weekend and Van Gaal knows that his last chance to win a title with United may well hinge on how his side cope with him.
United's defence fell apart in a 3-0 defeat at Tottenham Hotspur on Sunday, conceding three times - also in six minutes - and all but scuppering their hopes of Champions League qualification as well as raising more questions about Van Gaal's future.
Any repeat of that at the Boleyn Ground on Wednesday and United's FA Cup ambitions will vanish and the odds on Van Gaal failing to see out his three-year contract will shorten.
“I saw the Andy Carroll show (against Arsenal),” the Dutchman told reporters. “Carroll has special qualities and we have seen that in the match at Arsenal.
“Arsenal have great central defenders but still he could do that. We have to cope with Andy Carroll.”
Van Gaal accused his defenders of failing to communicate properly at Tottenham and says they must quickly recover from that beating.
“I hope we improve because this game is very important for us, it's the last chance for a title, very important for the players, the club, the manager and the fans.
“We have to recover mentally because Spurs was a blow. Everyone knows this is the last chance.”
West Ham manager Slaven Bilic will be tempted to start with the injury-prone Carroll against a vulnerable United side who may have forward and skipper Wayne Rooney on the bench after his recovery from a knee problem.
But United must not be pre-occupied with the player Bilic describes as probably the best header of a ball in the world, according to Van Gaal, whose side still have an outside chance of qualifying for the Champions League.
“It's not just Carroll, they have other players and a certain player called (Dimitri) Payet, and Manuel Lanzini who can score goals,” he said. “It's always difficult to cope with these kind of players.”
Payet scored a magnificent free kick in the original tie at Old Trafford last month before Anthony Martial equalised late on to earn United a replay.
Original source: ‘United must prepare for Andy Caroll show’