Nantes plan to appeal their FIFA transfer ban at the Swiss federal court, club president Waldemar Kita has confirmed.
The Court of Arbitration for Sport (CAS) yesterday upheld an embargo imposed by FIFA over the signing of Guinea striker Ismael Bangoura.
It means that the eight-time French champions cannot sign players either this summer or next January.
Kita told L'Equipe: "Our lawyers will undertake without delay an appeal to the Swiss federal court.
"By the end of the week, the appeal brief will be filed to defend the rights of a worker (Bangoura) who was prohibited from doing his job.
"We have to defend him and defend ourselves."
The ban relates to Nantes's acquisition of Bangoura from Al Nasr Sports Club of Dubai in January 2012.