Spanish giants Real Madrid and Atletico Madrid have been banned from registering players for the next two transfer windows.
They have been punished by world governing body Fifa for breaching rules over the transfer of minors – and Atletico say they will appeal.
The ban does not cover the current January transfer window.
Atletico were fined 900,000 Swiss francs (£622,000), while Real were told to pay 360,000 (£249,000).
“Our club is not in agreement with the sanction from international football’s governing body and will study all the documentation we’ve received to present an appeal against the sanction,” said an Atletico statement.
Real Madrid have yet to comment.
Barcelona were given the same penalty in April 2014 for also breaching rules on the transfer of under-18 players.
Their ban, which ended this month, did not stop the La Liga side from signing players.
They bought Arda Turan and Aleix Vidal in the summer of 2015, though both players were prevented from playing until the current window opened.
The next two transfer windows are July/August 2016 and January 2017.
Where does this leave Real Madrid?
BBC Sport’s Simon Stone: “David de Gea, Cristiano Ronaldo, Gareth Bale, Sergio Aguero.
“All four have been linked with transfers involving Real Madrid, all four – and anyone else for that matter – could be affected by today’s announcement.
“If they want to revive their interest in De Gea, whose deadline-day transfer from Manchester United last summer collapsed as the paperwork was not completed on time, or pursue Manchester City striker Aguero, Real will do so knowing they could not play until the 2017-18 season.
“Equally, if they decide to sell a Galactico in Ronaldo or Bale, both of whom have been linked with Manchester United, Real know they cannot then bring in a high-profile replacement and immediately play them.
“On the face of it, it leaves the Spanish superpower in a state of flux, with new coach Zinedine Zidane only able to promote from within.
“Quite handy, therefore, they have secured 19-year-old Marco Asensio (currently on loan at Espanyol) from Mallorca, Jesus Vallejo, 19, who has returned to Real Zaragoza on loan and 17-year-old Norwegian Martin Odegaard from Stromsgodset.
“Odegaard is now in the Real Madrid B team Zidane managed before replacing Rafael Benitez as coach of the main side.
“Worth noting as well that Real Madrid do have a couple of options. They could spend the next 18 days on a recruitment campaign as the ban does not take effect until after the current window is closed. Or if they appeal against the sanction it will delay its implementation. Barcelona did this in 2014 and used the time to sign Luis Suarez from Liverpool.”