The Belgian youngster proved to be the match-winner for United when scoring the only goal of their win over Aston Villa at Villa Park on Friday night and to become less on the periphery, van Gaal has implored Januzaj to add a little more substance to his game.
"Last year he had eight starts and 14 sub appearances. To say he hasn't had chances isn't a fair assessment," van Gaal said ahead of Tuesday night's Champions League qualifying play-off with Club Brugge.
"He had to compete with 24 players last year, and he is 20 years old. The characteristics of a young player are that he's not consistent and he has to show that this season.
"It's possible, but at a club like United, you never have a guarantee of a position in the top 11. Every player here knows that, and because of that we have a very good team spirit."