Cardiff City are set to claim the deal to buy Emiliano Sala from Nantes for £15m was not legally binding.
The Bluebirds are refusing to make interim payments for the striker, who died in a plane crash on 21 January.
Cardiff to argue Sala transfer was invalid
Cardiff will tell world footballs governing body Fifa that Nantes conditions for completion of the deal were not fulfilled and Sala was not registered as a Premier League player.
The Argentine died when an aircraft piloted by David Ibbotson, who is still missing, crashed into the English Channel near Guernsey.
A club spokesperson was quoted in the Daily Telegraph as saying: FC Nantes has completed all the required paperwork to complete the Emiliano Sala transfer. Thus, Fifa registered the international transfer certificate on 21st January 2019 at 5.30pm. Nantes is fully compliant with Fifa rules.
A Cardiff source said the transfer agreement stipulated – at the request of Nantes – that the Football Association of Wales and Frances Ligue de Football Professional had to confirm the registration to both clubs by 22 January, along with confirmation of the international transfer certificate being released.
The Bluebirds insist the terms of the contract maintains that if any parts of that arrangement were not confirmed, then the deal would be null and void.
It is thought the notifications clause was inserted because if the deal fell through, both Cardiff and Nantes would have had time to seek a new player before the January transfer window closed on 31 January.
BBC Sport has also learned arrangements for a signing-on fee did not meet Premier League rules and so had been rejected by the league.
A Cardiff spokesman would not comment on specific details but said: The club is aware of Fifas request for a response by 3 April and is processing that accordingly. We have no further comment at this stage.
Nantes say they completed all the necessary paperwork and have pointed out Fifa registered the international transfer certificate on 21 January.
Cardiff City will tell FIFA that the contract to sign Emiliano Sala from Nantes was not legally binding.
The Welsh club have refused to pay the £15m transfer fee for the striker, who was killed in a plane crash two months ago.
Cardiff will argue that Salas contract had been rejected by the Premier League and was therefore null and void.