Earlier today Nantes reportedly demanded the £15 million transfer payment from Cardiff City.
According to Sky Sports News, Cardiff have not yet paid any of the £15m fee agreed for the Argentine striker.
The Piper Malibu plane has since been spotted on the seabed off Guernsey, where a body was seen inside the wreckage of the aircraft, but has yet to be identified.
The Mirror reports that Nantes sent Cardiff an email last Thursday and followed up with a legal threat on Tuesday.More news: Boston Fans Bask In Victory After 6th Patriots Super Bowl Win
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Cardiff City have been left stunned after Nantes demanded payment for the £15million transfer of Emiliano Sala, who is missing and feared dead, after his flight went off-radar on a journey from France to Cardiff. BBC have attempted to speak to Nantes for a comment.
Remotely operated Vehicles (ROVs) were used in "challenging conditions" to pull the body out of the water "in as dignified a way as possible" the Air Accidents Investigation Branch (AAIB) said on Wednesday night.
The plane carrying Sala, 28, and Ibbotson, from Crowle, Lincolnshire, disappeared on route to Cardiff on 21 January after the footballer returned to Nantes to say goodbye to his former teammates.
Air accident investigators have confirmed that an attempt to recover the body found in the wreckage has begun.
Bordeaux, Sala's previous team, are thought to be due 50% of the transfer fee as per the terms of the deal which had taken him to Nantes.