Nantes have demanded payment of the £15m transfer fee for Emiliano Sala to join Cardiff City.
The 28-year-old striker who is presumed dead, went missing with Sala and pilot David Ibbotson on board two weeks ago.
Investigators have found the plane in the English Channel with a body inside, which is yet to be identified because of the poor weather.
They are also trying to establish who owned the plane, insurance issues and other details surrounding the flight which may mean it results in an insurance pay out.
According to Sky Sports, Nantes are threatening legal actions against Cardiff over the Emiliano Sala transfer.
Nantes sent an e-mail demanding the £15m fee last Thursday and followed up with a legal letter on Tuesday, threatening further action unless they get the first payment – the fee is spread over three years – within ten days.
French club Bourdeaux are also entitled to a cut of the fee, thought to be 50% – Sala was on their books from 2012 to 2015 before joining Nantes.