Cardiff face a three-window transfer ban unless they pay the first instalment of the transfer fee for Emiliano Sala to Nantes.
The Argentinian, 28, died when the light aircraft he was travelling in from France to the UK crashed into the English Channel on 21 January of this year.
Cardiff and Nantes were unable to reach an amicable conclusion on the financial aspects of the move, so the case came before the players' status committee (PSC) of world governing body FIFA.
It was announced by FIFA on 30 September that Cardiff had been ordered to pay the first instalment of Sala's transfer fee - €6m.
Documents published on Thursday, detailing the grounds for the decision, show that failure by Cardiff to pay the fee within 45 days of receiving bank details from Nantes following the ruling would mean "a ban on registering new players, either nationally or internationally, up until the due amounts are paid and for the maximum duration of three entire and consecutive registration periods".