Wales reported the French club have threatened legal action if the £15 million (NZ$28m) is not paid within the next 10 days.
Cardiff's first payment would ordinarily be due within seven days of the player signing, but the club do not intend to make any payments until the conclusion of official investigations into the causes of his disappearance.More news: The State of Our Union Is ______ ?
Sala and pilot David Ibbotson have been missing since the Piper Malibu aircraft disappeared from radars shortly after the take-off on January 21 en route from Nantes to Cardiff.
Reports of Nantes' demands come amid the discovery of a body aboard the wreckage of the plane.
However, Cardiff are yet to pay the first installment with the club still mulling over the details of the contract especially regarding recent developments surrounding the tragic incident.More news: Kristaps Porzingis SHOCKS Knicks in showdown talks amid Anthony Davis rumours
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.
They are also keen to discover why Sala's plane reportedly tried to take off on three separate occasions, before beginning its final journey towards Cardiff.
It is also reported that Bordeaux are entitled to a cut of the fee for Argentinian striker Sala, who was on their books from 2012 to 2015 before joining Nantes.More news: Gunners enter race to sign Idrissa Gueye ahead of PSG