Belgium's Vermaelen suffers hamstring strain
Vermaelen was substituted after 31 minutes as Belgium booked their place in the last 16 with a 1-0 win over Russia on Sunday - Divock Origi coming off the bench to net a late winner.
And the Royal Belgian Football Association have confirmed the Arsenal man has already started his rehabilitation.
Jan Vertonghen took Vermaelen's place in the contest against Russia at the Maracana, and could be in line for a starting berth should his colleague be unable to feature.
Belgium can secure top spot in Group H with a draw against South Korea, who need a win to have any chance of qualifying.
The winner of the group will face the runner-up from Group H - a spot currently occupied by the United States.