Lukaku has hardly been seen since his summer switch from Anderlecht.
"If Lukaku this season or next season is not playing, his career is threatened by oblivion," Vandenbergh told Voetbal Primeur.
"No one will even talk about Lukaku when he's not in the first team. That's the risk you take when you go to a team like Chelsea which attracts the best in the world.
"Lukaku is very young and needs time.
"At Anderlecht Lukaku still had much to learn. He was playing in the Europa League, now he sits in the stands every week."