The 28 year old died in a plane crash in January while travelling from France to join his new club.
Fifa has released the full reasons for its September ruling ordering Cardiff to pay the first 6m euros (£5.3m).
Cardiff will lodge an appeal against the decision in the next two weeks to the Court of Arbitration for Sport.
The Championship club have argued they were not liable for any of the fee because the Argentine was not officially their player when he died.
The world governing body's players' status committee (PSC) ruled Cardiff must pay the sum "corresponding to the first instalment due" in the transfer agreement and rejected the Welsh club's arguments on a variety of grounds.