The Belgian international, who joined the Canaries in the summer, had to come off at half time after starting his first league game at Sheffield Wednesday.
"Vadis has twisted his knee which is not great," manager Neil Adams told BBC Radio Norfolk.
"We're speculating on how bad it is. He said he turned out of a tackle and he felt some movement in his knee."
The game ended goalless at Hillsborough, extending Norwich's winless run to five games.