Catalan separatist organisation Tsunami Democratic are planning widespread disruption for the rescheduled El Clasico date.
The match had been scheduled to be played at Barcelona’s Camp Nou stadium on 26 October but due to the current volatility of the Catalan political situation, La Liga asked that the game be reversed to Real Madrid’s Santiago Bernabeu stadium.
That proposal was rejected by both clubs involved and with such a fluid period of unrest in Catalonia, the match was instead pushed back to 18 December.
There are fears that a high-level demonstration could take place on the day of the rescheduled game following this new statement.
“Tsunami Democratic is aware of the importance of the game between Barcelona and Real Madrid for fans of the sport,” Tsunami Democratic said in a statement.
“But this is an exceptional political situation. With people jailed, exiled and without [the right] to self-determination or their fundamental rights, there is no normality.
“Everyone must understand that all parties need to sit down and talk about freedom, fundamental rights and the right to self-determination in Catalonia.
“We call for a day of mobilisation on Dec. 18 and call on all citizens to reserve that date and come to Barcelona.”
Spain's Supreme Court sentenced nine Catalan separatist leaders to between nine and 13 years in prison for sedition over their role in an independence referendum in 2017.
Oriol Junqueras – the former vice-president of Catalonia and the highest-ranking pro-independence leader on trial – was handed the longest sentence of 13 years for sedition and misuse of public funds.
The prosecution had sought up to 25 years in prison for Junqueras but he, alongside the eight others, were cleared of a more serious charge of rebellion.
Following the court's verdict, Catalan independence supporters marched in Barcelona displaying banners that read "free political prisoners" while urging others to "take to the streets".