Manchester United midfielder Marouane Fellaini may have suffered ligament damage on Saturday, Belgium manager Roberto Martinez said after their 4-3 World Cup qualifying win.
Fellaini lasted just 30 minutes against Bosnia and Herzegovina before limping off with a knee injury.
With Belgium leading 1-0, Fellaini pulled up and, after receiving attention from Belgium's medical team, was replaced by Leander Dendoncker.
Martinez suggested the injury was serious after the game, saying: "We are all worried about Fellaini. We fear that there's ligament damage."
The Belgian FA also confirmed the injury, saying: "It is something to be worried about on first sight.