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FIFA has banned Real Madrid and Atletico Madrid from registering new signings for the next two transfer windows for breaching its rules on the international transfer and registration of players aged under 18.
The ban does not affect the current registration period and does not prevent players leaving either club, but means that after this month's transfer window closes neither Real or Atletico will be able to register any new players until the summer of 2017.
Atletico have also been hit with a 900,000 Swiss francs fine (?620,000) while Real have been fined 360,000 Swiss francs (?250,000).
A FIFA statement read: "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.
"Additionally, Atletico Madrid and Real Madrid have been fined CHF 900,000 and CHF 360,000 respectively, while both clubs have been issued with a reprimand and given 90 days in which to regularise the situation of all minor players concerned."