A Catalan separatist organisation has called for protests on the day Barcelona and Real Madrid are due to meet at Camp Nou in the first Clasico of the season.
The two sides were supposed to play each other on Oct. 26 but La Liga and the Royal Spanish Football Federation (RFEF) postponed the game due to political unrest in Barcelona at the time.
Protests were being carried out across the city following a court's decision on Oct. 14 to jail nine separatist leaders from Catalonia over their role in a failed bid for independence from Spain in 2017.
Further demonstrations, organised by the group Tsunami Democratic, had been arranged for the day of the game, which was the driving force behind the decision to call off the match.
Barca and Madrid subsequently struck an agreement with the RFEF for the game to rescheduled for Dec. 18, with Tsunami Democratic now threatening more disruptions in the city on the new date.
"Tsunami Democratic is aware of the importance of the game between Barcelona and Real Madrid for fans of the sport," the organisation said.
"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."
Police in Barcelona have yet to respond to the Tsunami Democratic statement, while no one from La Liga or the RFEF was immediately available for comment. A source close to Barcelona said the club would wait for more information before making any comment.
Real Madrid coach Zinedine Zidane was asked about it in a news conference on Friday ahead of his side's trip to Alaves. He said he would do as instructed on the day of the game.
"We're counting on playing [the Clasico], but when the moment arrives we will see," he said. "It's not for me to say if it's going to be played or not.
"On Dec. 18, we have to be there to play. We will see what happens down the line. What I'm focused on is Saturday's game."