Ecuador finished fourth in South American qualifying to grab the continent’s last automatic berth for the mega event. It was drawn into a group with Qatar, the Netherlands and Senegal.
Castillo did not take part in games against fifth-place Peru or sixth-place Colombia.
FIFA mentioned it has asked the Peruvian soccer association to submit its position on the Castillo case as well.
Irrespective of the result of the case, Peru could yet qualify for the World Cup as it is set to play an intercontinental playoff game against United Arab Emirates or Australia on June 13 in Doha.
After Chile filed an official protest saying that Byron Castillo is Colombian and should not have been permitted to represent Ecuador in eight qualification games, FIFA launched a disciplinary process. Ecuador now faces forfeiture of those matches, including a win and a draw against Chile.
Chile finished seventh, but could vault into the qualifying places if it was awarded six points from its games against Ecuador, along with the better goal difference.
The FIFA investigation will have a look at the “allegations concerning the possible falsification of documents granting Ecuadorian nationality to the player,” soccer’s governing body said.
A FIFA ruling is likely needed within a month, ahead of the intercontinental playoff matches.
Ecuador’s soccer federation previously rejected Chile’s claims and insisted that Castillo is legally an Ecuadorian citizen. Castillo mostly plies his trade as a right back, but is also capable of playing as a right winger. Castillo played in eight of Ecuador’s 18 qualifying matches, in which it picked up 14 of their 26 points.