Nantes have demanded the first payment from Cardiff City for the purchase of Emiliano Sala, according to a report.
The Argentine striker became the Bluebirds' club-record signing when joining in a £15m deal last month.
Sala, along with pilot David Ibbotson, is missing presumed dead, however, as the plane he was travelling in between the two cities lost radar contact near Guernsey 16 days ago.
In the wake of the tragic incident, Cardiff have withheld the first scheduled payment - believed to be £5m - until both the Air Accidents Investigation Branch and the police conclude their investigations.
BBC Sport reports that Nantes are threatening legal action, though, and they have given Cardiff 10 days to hand over the money, a slice of which will go to the player's former club Bordeaux.
The report indicates that City fully intend to honour the contract, but that may be months down the line.
Attempts have been made this week to recover a body from the plane that was carrying Sala and Ibbotson.