Cardiff City have been threatened with a three-window transfer ban by FIFA if they fail to pay the first installment of the fee owed to Nantes for the late Emiliano Sala.
The FIFA Players' Status Committee ruled in September that Cardiff must hand over a €6 million (A$9.7m) payment for club-record signing Sala, who, along with pilot David Ibbotson, died when their Piper Malibu aircraft crashed in January.
Sala had accepted a move but Cardiff claimed the agreement to pay Nantes £15m was not legally binding because conditions insisted upon by the selling club were not fulfilled.
Cardiff announced in a statement last month that they intend to appeal at the Court of Arbitration for Sport, but world football governing body FIFA has outlined its reasons and ordered the Welsh side to pay up.
FIFA confirmed in a 21-page document published on Monday that the threat of a ban, which would run through until the end of the 2020-21 campaign, will be lifted if Cardiff make the payment within 45 days.