The two teams go head to head in Sao Paulo tonight with a place in Sunday's final against Germany on the line.
While admitting that Messi is a "very important player" for the South Americans, Van Gaal believes that the whole of the Argentine side are worth monitoring.
"I'm not thinking about individual players, I'm thinking always that we have to play against a team, but Messi is a very important player," he told FIFA.com.
"So we have to play against Argentina and we have to try to stop Messi getting the ball, passing the ball, scoring goals, and you do that as a team. I hope my team can do the job."
Messi has scored four goals in five games for Argentina so far at the tournament.