The 28-year-old was on his way to Wales from France after Cardiff had agreed a deal worth £15m to sign the striker.
Cardiff has since insisted they should not be liable to pay for Sala as he had not been registered by the Premier League and was not officially their player at the time of his death.
But FIFA’s player status committee this week ruled that the Bluebirds must pay Nantes the amount equivalent to the first instalment of the fee – £5.3m.
Cardiff, who were relegated from the top-flight last term, have now announced that they will challenge that ruling at the Court of Arbitration for Sport in Lausanne, Switzerland.
“Following FIFA’s update on their announcement regarding the transfer of Emiliano Sala, Cardiff City Football Club will be launching an appeal to the Court of Arbitration for Sport,” read a statement from the club.
“Cardiff City FC is extremely disappointed at the decision of the Players Status Committee to award against the club. It would appear the committee has reached its conclusion on a narrow aspect of the overall dispute, without considering the full documentation presented by Cardiff City FC to FIFA.
“Nevertheless there remains clear evidence that the transfer agreement was never completed in accordance with multiple contractual requirements which were requested by Nantes, thereby rendering it null and void.
“We shall be appealing to CAS in order to seek a decision which considers all of the relevant contractual information and provides clarity on the full legal situation between our two clubs.
“This is a complex matter, which includes ongoing civil and criminal considerations both in the UK and abroad, which will likely have an impact on the validity of the transfer. It is therefore vital that a comprehensive judgement is reached following a full assessment and review of the facts.”