Nantes have begun legal action against Cardiff City, demanding the first payments for the purchase of Emiliano Sala, understood to be in excess of £5m, is transferred immediately, Sky Sports News understands.
Cardiff have not yet paid any of the £15m fee for the Argentine striker, according to Sky sources.
Sky Sports News understands the club feels it necessary for the salvage operation in the Channel to be concluded and for both the Air Accidents Investigation Branch (AAIB) and the police to conclude their investigations before any payments are made.
Privately Cardiff believe there are a series of questions that still need answering, most notably about the ownership of the Piper Malibu aircraft which crashed North of Guernsey on January 21.
They are also keen to discover why, if as has been suggested, Sala's plane tried to take off on three separate occasions before beginning its final journey towards Cardiff.
After a series of phone calls from the French club, Sky Sports News understands Cardiff received the first letter from Nantes' lawyers more than a week ago. The Premier League club's lawyers have responded, asking for more time.
At this stage it is not known whether any legal case would be heard in France or the UK.
We have attempted to contact Cardiff who have so far not responded.