Spain - Clement Lenglet describes it as the fixture that "freezes time" and believes this week's Clasico double-header could still define the seasons of both his own Barcelona, and Real Madrid.
The two clubs will meet twice in four days at the Santiago Bernabeu, on Wednesday in the second leg of their Copa del Rey semi-final and then on Saturday, in a battle of first against third in La Liga.
Even victory is unlikely to project Madrid back into the title race but for Santiago Solari's side, momentum is at stake, their steady, if not unwavering, resurgence poised for a potential double boost ahead of the campaign's decisive months.
Barcelona's priority may be the Champions League and their hold on La Liga too tight to shake off but it says something for the magnitude of the Clasico that Lenglet still feels its significance.
"This month is pivotal," he says, in an exclusive interview with AFP.
"There is the Champions League and these two games against Real, when we can qualify for a cup final and then gain or lose points on them in the league.
"We have to manage them properly. It could be pivotal for the rest of the season."
Madrid hold a slight advantage in the cup, having taken a creditable 1-1 draw from the opening leg last month at the Camp Nou.
Barca were without Lionel Messi, whose stunning hat-trick against Sevilla on Sunday was surely one of his best, but Madrid's showing confirmed their transformation from the broken team that were thrashed 5-1 by the Catalans in October.
"The dynamics are completely different now," says Lenglet. "These are the European champions. They have turned the tide."
- Greatest grudge match -
Madrid and Barca look under threat in the Champions League from the likes of Manchester City, Liverpool, Paris Saint-Germain, Juventus and Atletico. Yet in terms of quality, the Clasico remains football's greatest grudge match.
"As players, we are in our little bubble but when we come out, we realise it is a different game from the others because of the power it has around the world," Lenglet said. "It's a game that seems to freeze time."
Lenglet is in a position to appreciate it more than most. Only three seasons ago, the 23-year-old was playing for Nancy, the French club where he was first given his chance.
He spent 18 months at Sevilla, enough to persuade Barca to pay his 35.9 million-euro ($40.6 million) buy-out clause last summer.
"I could never have imagined I'd come so far so quickly," he says. "I went to Seville, and for me that was a big jump.
"No disrespect to Nancy, but they were worlds apart. To then be at Barcelona a year and a half later, I could never have imagined it."
He has been thrown in at the deep end, with Samuel Umtiti only just recovering from a knee injury, allowing Lenglet to be fast-tracked into the role of Gerard Pique's partner-in-chief.
Many are predicting a call-up to the France squad next month.
"We live with the best players in the world and that makes you learn quickly," Lenglet said.
"I'm more thoughtful now about when to release the ball, when to clear and when to keep it, when to be more patient. It's about managing the game."
It helps to have Messi too, Barcelona's captain fresh from scoring his 50th career hat-trick last weekend.
"I remember when I first arrived, he said hello, gave me a little hug - I felt immediately at ease," Lenglet said.
Messi may not play both games against Madrid, after being disrupted recently by a thigh strain, but his influence on youngsters like Lenglet is total.
"He is a technical leader," said Lenglet.
"On the field he makes the difference so often, in almost every game. He's a leader through his experience. He watches football, knows all types of football and has mastered it to perfection.
There's only one Messi and when he gives advice, you listen."