Fifa on Thursday banned Real Madrid and Atletico Madrid from buying players for one year over their dealing in under-age players.
The ban will start from the July transfer window this year and finish with the January transfer market in 2017.
Atletico were also fined 900,000 Swiss francs (820,000 euros) and Real 360,000 (330,000 euros).
“The two clubs were found to have violated several provisions concerning the international transfer and first registration of minor players as well as other relevant provisions with regard to the registration and participation of certain players in competitions,” said a Fifa statement.
Barcelona has just ended a one year ban for similar reasons.
Real and Atletico were “issued with a reprimand and given 90 days in which to regularise the situation of all minor players concerned,” Fifa said. They can still sell players during the transfer ban.
Fifa said the alarm was raised over the two clubs by Fifa’s Transfer Matching System and its disciplinary committee completed the inquiry.
Under international football rules, players under 18 cannot be transferred to another country, except in limited circumstances. All transfers need the approval of a special Fifa committee.
“The investigations concerned minor players who were involved and participated in competitions with the clubs over various periods between 2007 and 2014 (Atletico Madrid) and between 2005 and 2014 (Real Madrid),” Fifa said.
The ban follows a similar sanction handed to European champions Barcelona, who were unable to register new players during 2015.
Barca were initially banned in April 2014, but managed to delay the sanction taking affect until the transfer windows in January and the summer 2015 by launching an ultimately unsuccessful appeal to the Court of Arbitration for Sport (CAS).
By delaying the ban, Barca managed to sign the likes of Luis Suarez and Ivan Rakitic in the summer of 2014 to propel them to a treble of La Liga, Champions League and Copa del Rey.
The news is just the latest institutional embarassment for Real Madrid just over a week after they appointed French legend Zinedine Zidane.
Madrid have sacked two Champions League winning coaches in Carlo Ancelotti and Rafael Benitez in the past seven months, as well as being thrown out of the Copa del Rey for fielding an ineligible player.
The sanction could also be bad news for the likes of Paris Saint-Germain and Manchester United, who had targeted Madrid stars Cristiano Ronaldo and Gareth Bale with Real highly unlikely to dispose of their best players without the chance to sign suitable replacements.
La Liga leaders Atletico Madrid’s usually hectic transfer policy will also be put on hold. However, Diego Simeone’s men look better placed to cope with the ban having invested heavily in young talent over the past year.
Neither Real no Atletico made an immediate comment on whether they would appeal.