Zurich - Barcelona will not be able to sign any new players until January 2016 after world football's governing body FIFA rejected an appeal over a transfer ban imposed for breaching rules on underage players.
The Catalan giants will be banned from the national and international market for two consecutive transfer windows, starting in January 2015, FIFA said.
Barcelona immediately announced they would appeal to sports' highest court, describing the decision as an "affront" to its youth training academy.
"FC Barcelona announces that it shall continue defending its interests before the highest sporting authority, in this case the Court of Arbitration for Sport", the club said in a statement.
FIFA slapped on the sanction in April, after ruling that Barcelona and the Spanish Football Association had failed to respect regulations governing the international transfer of players under the age of 18 to the club, and their participation in national competitions.
But the fact that Barcelona filed an appeal put the punishment on ice, allowing to club to snap up a string of names over the summer transfer period.
They include Uruguay international Luis Suarez, bought from English powerhouses Liverpool, though he is not eligible to play until October 25 because he is serving a ban for biting an opponent during the World Cup in June.
FIFA's April decision came after a probe conducted the previous year by FIFA Transfer Matching System -- its market watchdog, which was set up in 2007.
The investigation concerned several youths who were registered and participated in competitions with Barcelona over various periods between 2009 and 2013.
The rules of global football set 18 as the minimum age for international transfers of players, and while there are limited exceptions, they are only allowed if a special FIFA committee gives a green light.
The aim, FIFA says, is to protect minors, given that young footballers can be particularly vulnerable to exploitation and abuse in a foreign country without the proper controls.
Barcelona were ruled to have breached the rules in the case of 10 players, and to have committed several other infringements in the context of others.
FIFA did not identify the players by name.
In its decision on Wednesday, FIFA also upheld Barcelona's 450 000-Swiss-franc fine, and gave the club 90 days to "regularise the situation" of all the minor players concerned.
It also left in place the 500 000-Swiss-franc penalty imposed on the Spanish FA and gave it one year to shake up its regulatory framework and existing system concerning the international transfer of minors in football.