Nice have been prevented by FIFA from registering new signing Hatem Ben Arfa (below).
The playmaker, a free agent after his release from Newcastle, joined Le Gym last Monday but was not available for Saturday's win over Lorient as he awaited international clearance.
The problem was due to the clause in FIFA's transfer regulations which states a player cannot play for more than two clubs in the same season.
Article 5.3 of FIFA's regulations on the status and transfer of players states: "Players may be registered with a maximum of three clubs during one season. During this period, the player is only eligible to play official matches for two clubs."
Ben Arfa made eight appearances on loan at Hull - and an appearance for Newcastle's under-21 side earlier in the season has been ruled by FIFA to be an 'official' match.
A statement on Nice's official website read: "OGC Nice have received a copy of a correspondence sent by FIFA to the FFF (French Football Federation). The international federation responded to the question posed by the French federation regarding a match played by Hatem Ben Arfa with Newcastle Under-21s.
"Contrary to the position of the English (Football Association), it appears that for FIFA the match in the U21 Professional Development League 'must be considered as official in the sense of the regulation' and 'must therefore be taken into consideration in determining the application of article 5.3 of the regulation' on the status and transfer of players."
The development leaves Ben Arfa, who has 13 France caps to his name, in limbo.
Hull pulled the plug on his loan deal after he fell out of favour with manager Steve Bruce.