Real Madrid are "obliged" to beat Barcelona on Saturday (1200GMT) if they are to maintain any hope of retaining their La Liga title, according to Real captain Sergio Ramos.
The European champions picked up a record fifth trophy of the year to cap a fine 2017 at the Club World Cup last weekend, but trail Barca by a mammoth 11 points at the top of La Liga albeit with a game in hand.
"It will be a massive game," said Ramos. "It is the biggest game in the world.
"We are obliged to win more than ever for the situation we are in to try to keep ourselves in the fight for La Liga."
For the first time an El Clasico will kick-off at lunchtime as La Liga seeks more attention from Asian viewers.
And the worldwide audience could be treated to the return of Cristiano Ronaldo, Karim Benzema and Gareth Bale together for the first time this season.
Real's 'BBC' front three haven't played a single minute of action together, largely due to a series of injury problems for Bale.
However, the Welshman returned to play his part in the Club World Cup success with the semi-final winner over Al Jazira.
Ronaldo is also "100 percent" fit to play according to coach Zinedine Zidane despite the Portuguese returning to training with the rest of his teammates for the first time this week on Friday.
"He is 100 percent, he trained today and that is all that interests me," said Zidane, who unlike Ramos has tried to play down suggestions Madrid must win to remain in the title race.
Madrid were the last side to beat Barca and in some style with a 5-1 aggregate thrashing in the Spanish Super Cup back in August.
But, since then, the Catalans have bounced back under new coach Ernesto Valverde to go 24 games unbeaten in all competitions.
To recover from Neymar's departure to Paris Saint-Germain for a world record fee, Barca have become ever more reliant on the brilliance of Lionel Messi and the Argentine has responded with 18 goals already this season.
"It will be important for us to win this game for what it means," said Messi as he picked up his award for being the top scorer in La Liga last season this week.
"A game against Madrid is special, it is at their place and we would take a significant advantage over them if we win."
The tension on the field could be accompanied by an even more hostile atmosphere for Barca than normal in the capital in the wake of regional elections in Catalonia.
Three parties favouring independence for the region from Spain retained an absolute majority in the Catalan parliament on Thursday.
However, Valverde played down concerns as Barca also visited to Madrid to face Atletico Madrid in October without problems amid heightened political tension following violent clashes in a banned independence referendum called by separatists.
"The atmosphere tomorrow will be good, I have no doubt about that," he said.
"We went to play at Atletico Madrid close to October 1 when there was a lot of talk about the reception we would get and I think as a football man it is one of the best atmospheres I have seen. There was a good feeling between the teams, the fans and I expect tomorrow will be the same."
Once again shorn of injured French duo Samuel Umtiti and Ousmane Dembele, Valverde is expected to make just one change from the side that started last weekend's 4-0 win over Deportivo la Coruna with Sergio Busquets replacing Paco Alcacer.