BBC Sport has revealed French club Nantes have demanded payment from Cardiff for striker Emiliano Sala who went missing after a light aircraft crashed into the English Channel.
Sala, along with pilot David Ibbotson, was on board the Piper Malibu N264DB which lost radar contact near Guernsey on 21 January.
The Argentine striker was Premier League club Cardiff's record signing at a fee of £15 million.
Cardiff have withheld the first scheduled payment until they are satisfied with the documentation.
It is understood Nantes are threatening legal action if they do not receive a payment within 10 days.
Cardiff said the club is "surprised" Nantes have made the demand while attempts are being made to recover a body from the plane wreck that was carrying Sala and pilot Ibbotson.