Earlier on Tuesday it was suggested the 22-year-old had sustained an ankle injury and was taken to hospital, making him doubtful for the Group A leaders' match with Croatia on Friday.
De Bruyne wrote on Twitter: "Just to say. I'm fully fit for the game against croatie. No injury at all."
De Bruyne is a key figure for the Red Devils, who need a point against the second-placed side in Group A to advance to next summer's finals in Brazil, despite being marginalised at Chelsea this term.
Chelsea manager Jose Mourinho has left De Bruyne out of his squad in recent weeks and is demanding more from the player who impressed on loan at Werder Bremen last season.