Belgium's World Cup captain Vincent Kompany missed team training on Thursday with a slight groin strain, coach Marc Wilmots said.
Belgium play Russia in their second Group H match on Sunday, but Wilmots did not indicate whether the Manchester City defender was a doubt.
"No Vincent Kompany in training today, slight groin strain," Wilmots said on his Twitter account. "He is working individually today with the medical staff!"
Playmaker Eden Hazard missed training on Wednesday, but was back in action with the squad on Thursday. Belgium beat Algeria 2-1 in their first match to lead the group.