I'd always assumed football year mate but based on zero info, you could well be right.
Not sure why they would stop them registering him though if it was calendar year.
The world governing body's transfer rules prevent a player from appearing for more than two clubs in one season.
The midfielder played eight games for Hull and one for Newcastle's under-21s earlier this season, with Fifa ruling the latter to be an official match.
The France international, a free agent after his release from Newcastle, joined Nice on 5 January, but was not available for Saturday's 3-1 win against Lorient as he awaited international clearance.
The delay centred around article 5.3 of Fifa's regulations on the status and transfer of players, which 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."
A statement on Nice's website confirmed the club had received a copy of correspondence sent by Fifa to the French Football Federation.
It said that contrary to the position of the Football Association in England, Fifa had classed the under-21 match for Newcastle United as "official".