Michy Batshuayi was carried from the pitch on a stretcher after suffering an injury at the end of Borussia Dortmund's Ruhr derby defeat to rivals Schalke.
Goals from Yevhen Konoplyanka and Naldo - the latter a sensational strike from a free-kick - earned second-placed Schalke a vital three points in the race for Champions League qualification.
And Dortmund's derby day ended in further disappointment as Batshuayi appeared to badly hurt his ankle in a heavy challenge from Schalke's Benjamin Stambouli.
Although the former Tottenham man won the ball, the Frenchman caught Batshuayi with the follow-through and left the Belgium striker writhing on the turf in obvious pain.
Batshuayi - who has hit seven Bundesliga goals since joining on loan from Chelsea on January - left the field on a stretcher, covering his face with his hands.
And with the World Cup less than two months away, Batshuayi's place in the Belgium squad may be in doubt if the injury is as severe as it appeared.