United will take on West Ham away from home at the Boleyn Ground in the Premier League on Tuesday evening.
England international striker Carroll could start for the Hammers in what is the last ever game at the Boleyn Ground.
Van Gaal has admitted that he is worried about his side facing the 27-year-old former Newcastle United and Liverpool man.
When asked about Carroll’s threat, Van Gaal told The Sun: “Yes. I am very worried about that. I am always organising. We always have a meeting about that, every game, and it also takes a long time to organise it well.
“We are normally the smallest team in the Premier League so we always have problems with set-plays. At Norwich you saw that. We have to cope with that and you are right, I can’t deny that.”
Carroll has scored nine goals and created 17 chances in 25 Premier League appearances for West Ham this season.
The Englishman has a pass accuracy of 62% and a shot accuracy of 56%, and has won 91 headers, five dribbles and three tackles.
West Ham are seventh in the Premier League table at the moment, while United are currently fifth in the standings and will clinch a Champions League place if they win their final two league matches.