FIFA have confirmed that FC Nantes have launched an official complaint over Cardiff's refusal to pay the £15 million transfer fee for Emiliano Sala.
Sala and pilot David Ibbotson died when the plane they were travelling in went down over the English Channel just two days after Cardiff had signed him.
Nantes' lawyers wrote to the Welsh club in early February asking for the first of three annual payments for the player to be made but Cardiff City said they wanted to wait for the investigation into the crash to be completed.
The deadline for payment was extended until February 26.
Having received no payment, however, the French side have carried out their threat to take the matter to FIFA's Dispute Resolution Chamber.
In a statement, a FIFA spokesperson said: "We can confirm that we have received yesterday evening a claim from FC Nantes against Cardiff City in connection with the transfer of Emiliano Sala. We are looking into the matter and consequently we have no further comments at this stage."
Cardiff said they remained "committed to ensuring fairness and accountability" over the deal, but insisted "the facts surrounding this tragedy" had to first be established.
The Air Accidents Investigation Branch released an interim report on Monday which left several major questions unanswered including whether the pilot David Ibbotson or the single-engine aircraft were licensed for commercial flights.
Any wrongdoing in regard to the flight could annul Cardiff's insurance policy for Sala and, if that wrongdoing was another party's responsibility, they may have to sue for compensation.
That could mean Cardiff having to take legal action against Willie McKay, the agent at the centre of the deal, although the Monaco-based Scot has repeatedly denied any wrongdoing and has told Press Association Sport the Premier League side are trying to "throw him under the bus".
Cardiff have not responded to McKay's claims.