Nantes have requested the first instalment of Emiliano Sala's £15million transfer fee from Cardiff City, according to a BBC report.
Sala, 28, who signed for Cardiff from Nantes on January 19 in a £15m deal, has been missing since January 21, when the plane he was travelling in with pilot David Ibbotson went down over the English Channel.
Its wreckage was pictured for the first time on Sunday afternoon after being discovered earlier that day, when the two search teams located the Piper Malibu aircraft.
Authorities say they are trying to recover the body spotted in the seabed wreckage of the plane. Authorities have not confirmed whether the body located by an underwater camera was Sala or pilot Ibbotson - the only people on board.
According to a report by BBC Wales on Wednesday, Nantes have threatened legal action unless they receive a payment from Cardiff within 10 days.
The report suggests that Cardiff witheld the first scheduled payment of Sala's transfer fee - with the full amount understood to be due over three years - until they were satisfied with the documentation, while the Welsh club said to be 'surprised' by the demand given the ongoing attempts to recover the unidentified body on the plane.
In a statement regarding the recovery efforts, the Air Accidents Investigation Branch (AAIB) cautioned that "strong tidal conditions mean we can only use the remotely operated vehicle for limited periods each day and this will mean that progress is slow."
Cardiff City and Nantes have both been approached for comment by Standard Sport.
