Cardiff City are to appeal to the Court of Arbitration for Sport after the FIFA Players' Status Committee ruled they must pay Nantes €6 million for the late Emiliano Sala.
The Championship club claim the verdict was reached "without considering the full documentation presented by Cardiff City FC to FIFA".
Sala, Cardiff's record signing, and pilot David Ibbotson died when their Piper Malibu aircraft crashed in January. The striker had accepted a move from Ligue 1 side Nantes but the Bluebirds claimed the agreement to pay Nantes a £15 million ($18m) fee was not legally binding because conditions insisted upon by Nantes were not fulfilled.