There were reports on Tuesday that De Bruyne was taken to hospital for assessment of an ankle injury suffered in training ahead of the game.
The Chelsea forward did not confirm or deny the reports but wrote on his Twitter page: "Just to say I'm fully fit for the game against Croatia. No injury at all."
Marc Wilmots' side go into their final two qualifiers against Croatia and Wales with a five-point lead in Group A.
A draw in Zagreb will guarantee a place in Brazil next summer, but Belgium are without the injured Manchester City captain Vincent Kompany.
De Bruyne started two of Chelsea's first three games this season but was left out of the squad for Sunday's trip to Norwich after criticism from Jose Mourinho.