Barcelona president Josep Maria Bartomeu claimed the club had been victims of "a great injustice" after their appeal against a two-window transfer ban was dismissed by the Court of Arbitration for Sport.
The Catalan outfit turned to CAS in August after Fifa rejected their appeal to overturn the ban, which was imposed by world football's governing body in April due to concerns over the "international transfer of minors''.
But their quest hit a further dead end yesterday morning, with the CAS ruling meaning they will be unable to sign any new players in 2015 - much to the dismay of Bartomeu.
"A great injustice has been committed: an injustice for Barca, for all the children and parents affected by this decision, for all the club members and for football in general," the president said.
"We have always made it clear that we consider Fifa's sanction to be disproportionate. This judgement by CAS, which ratifies Fifa's decision, is not good for us and defies all sporting logic."
Barca were found guilty of breaching Fifa's rules on the transfer of players aged under 18. The players in question were registered and participated in competitions with the Catalan club between 2009 and 2013.
Bartomeu has vowed to lead a campaign to change Fifa regulations.