Nantes must observe a 16-month transfer embargo after their appeal against the sanction failed at the Federal Supreme Court of Switzerland.
The Ligue 1 club were handed the punishment by FIFA and the Court of Arbitration for Sport (CAS) over the signing of striker Ismael Bangoura from Al Nasr in February 2012.
FIFA and CAS both ruled that Nantes had incited Bangoura to break his contract with the Dubai club.
In a statement on its official website, the Lausanne-based Supreme Court announced it had upheld the original verdict, meaning Nantes - currently 15th in Ligue 1 - are barred from making any signings during the next two transfer windows.
The club and Bangoura are jointly obliged to pay Al Nasr 4.5million euros in compensation while the Guinea international has already served a four-month ban.
Nantes can sell and release players but cannot register new signings with the French Football Federation until the summer of 2015.
Nantes president Waldemar Kita told Ouest France: "Where is the morality? The player was not being paid and could not train."