Chile's football federation (FFCh) has lodged a complaint with Fifa against Ecuador over the alleged ineligibility of full-back Byron Castillo.
Ecuador have qualified for the World Cup while Chile narrowly missed out.
But the Chilean federation has lodged a claim against Castillo over "use of a fake birth certificate, false declaration of age and false nationality."
Castillo, 23, played in both Ecuador's matches against Chile, a 2-0 victory in Quito in September 2021 and a 0-0 draw in November.
Chile finished seventh in the single South American World Cup qualification table, seven points behind Ecuador in the fourth and final automatic berth for Qatar.
If Fifa were to accept the challenge and award the two matches to Chile, they could potentially leapfrog into a direct qualification position.
Chile claim that Castillo, who represented Ecuador at both under-17 and under-20 level before graduating to the full national team, is in fact Colombian.
The FFCh's lawyer Eduardo Carlezzo told Television Nacional de Chile that their complaint proves "in a clear manner that the Ecuadoran birth certificate used by the player is fake and that, on the other hand, the Colombian certificate is real."
Carlezzo claimed the Ecuadoran federation carried out an investigation in 2018 and determined that Castillo was Colombian "in an official document, which we have sent to Fifa."
Ecuadoran press reports from April 2021, claimed the constitutional court had confirmed his nationality and rejected an appeal by the Civil Registry.
The reports mention rumors that Castillo was born in Tumaco, Colombia but says he received his official ID card in March 2021.
He made his debut for Ecuador's national side later that year in September, playing in eight World Cup qualifiers.
Ecuador won four, drew two and lost two of those matches.
Chile's complaint says "there are innumerous proofs that the player was born in Colombia, in the city of Tumaco on July 25, 1995, and not November 10, 1998 in the Ecuadoran city of General Villamil Playas."
Crucially, Castillo did not play against either Colombia or Peru, who finished in the two places immediately above Chile, meaning that should the complaint be upheld, they would like stand to benefit the most from any potential subsequent sanctions related to the eight matches.
Castillo began his career at Ecuadorans Norte America and now plays for the country's giants Barcelona SC.
Carlezzo said the submission to Fifa showed that Norte America "is the epicentre of fake documents for players" and that the civil registry in Guayas state, where Castillo was officially born, is "involved in criminal procedures for altering documents."