Ligue 1 club Nice announced on Thursday that they will lodge an appeal after FIFA refused to ratify the transfer of Yannick Djalo from Sporting Lisbon.
FIFA say that the deal for Djalo, 25, was not completed before the transfer deadline at midnight on August 31.
"The club will take whatever steps necessary to have this decision overturned as the transfer was registered by the French league before the deadline set by FIFA," read a statement on Nice's website.
Nice say the first documents relating to the deal arrived at the league at three minutes to midnight on August 31, with the last arriving at bang-on midnight.
The Portuguese international of Guinea-Bissauan origin is currently training with his new teammates as he awaits a final verdict on the case.