On Tuesday, some Barcelona fans mistakenly threw stones and bottles at their own bus as it made its way into Montjuïc. The huge club badge and massive “Barça” written on the side were not enough of a clue. In fairness, they might not have seen that through the crowd and all the smoke. As for the metaphor, the self-inflicted damage, that was harder to miss. By the end of the night, Barcelona were out of the Champions League, failing to reach the semi-final for a sixth successive season. Against Paris Saint-Germain they had competed, which genuinely was something, and Xavi Hernández was busy telling the referee, Istvan Kovacs, he had been a “disaster”. But if the official got blamed for the result, ultimately Barcelona had conceded four goals. At least in part, the club that created a crisis so bad they forced out the greatest player they ever had and invented the palanca, selling assets to survive, had done it to themselves. Xavi was sent off and so was the centre-back Ronald Araújo after only half an hour. PSG’s third goal came from the penalty spot after a challenge that João Cancelo, who committed the foul, admitted was “infantile”. Xavi was furious about Araújo’s red, but the goalkeeper Marc André ter Stegen watched it during the post-game interview and had to admit that, yes, it was a sending off. Ilkay Gündogan went further, questioning the wisdom of making the challenge in the first place. Going a man down that early killed them, he said. Defeated 4-1 by Real Madrid in the Spanish Super Cup final and 4-2 by Athletic Club in the Copa del Rey quarter-final and now out of Europe having conceded four more at home to PSG, Barcelona were left with only the league. And that too is on edge: on Sunday they travel to the Santiago Bernabéu, eight points behind their great rivals with seven games left. Lose and it is done, draw and it is done. Win and it is probably done, too. They are, as the Spanish line inspired by the Inquisition has it, clinging to a burning nail, desperately holding on. The surprise perhaps is that there is a chance at all. In January, Xavi resigned after a 5-3 defeat against Villarreal, describing the role of coach as “cruel and unpleasant”, but insisted on continuing to the end of the season. It was a formula that the president, Joan Laporta, said he accepted only “because it’s Xavi”; it is also, unexpectedly, a formula that has worked. Since then, Barcelona are unbeaten in 10 games in the league, picking up 26 of the last 30 points. In Europe, they found a way past Napoli and won in Paris. Xavi has repeatedly said that it was his decision to walk that changed everything, even if he has not explained exactly why. If that line appears in every press conference, so for the last few weeks has the question about him changing his mind and staying. President, vice-president and sporting director have all talked about convincing him to, not least because finding a replacement has not been easy. Besides, things were going well. Until Tuesday night, when Barcelona were beaten, that Barcelona again, and suddenly it all felt final again. Lose the clásico and it really will be. The following night, Real Madrid did what Real Madrid do, the contrast cruel in beating Manchester City in a penalty shootout: if there is a vulnerability about Barcelona, there’s an almost inexplicable invincibility to their rivals. Somehow, they always overcome, as if the problems that sink others barely touch them, a survival instinct no one else has, a capacity to resist; they are the T-1000 hanging on your back bumper. Holding on to that burning nail seems to come more naturally to them. They have been without Thibaut Courtois all season, without Éder Militão too. David Alaba suffered a ligament tear. Karim Benzema departed, a year ahead of schedule. Jude Bellingham wears heavy strapping on his shoulder, Vinícius Júnior tore a thigh. Against City, they faced 38 shots and somehow prevailed. There, Andriy Lunin, the back-up goalkeeper they were sufficiently unsure of to make the emergency signing of Kepa Arrizabalaga, made two saves and Lucas Vázquez, Nacho Fernández and Antonio Rüdiger scored their penalties. None of them were expected to be starters this season. Who starts on Sunday is another matter: this is a tired team, Carlo Ancelotti admits, though it refuses to crack. In the last clásico, they were outplayed for an hour or so, and then Bellingham appeared out of nowhere. If their issues are physical, Barcelona’s are more emotional. This is a clásico conditioned by Europe – not least because of an awareness that midweek mattered more, the league meeting arriving late on the agenda – and by the fallout from it. Cancelo told ESPN that he had received threats after his foul in midweek, that he had been unable to sleep. After Gündogan’s comments it was hard to avoid the feeling that faultlines had opened, just as Madrid appear steeled by it all. Gündogan had spoken out after the first clásico this season, expressing his disappointment that the 2-1 defeat to Madrid had not hurt more. “I would like more anger in the dressing room,” he insisted. This time, he suggested that Araújo would have been better letting Bradley Barcola go. His wife got involved, insisting that her husband’s attitude is that of a “treble winner”. Araújo said he preferred not to respond publicly but in effect did so when he justified it with the existence of “dressing room values and codes” he would not break. Suddenly, it was everywhere, overshadowing everything. “It’s more of a noise outside than inside; Gündogan wasn’t trying to single anyone out,” the captain, Sergi Roberto, insisted. “He didn’t mean any harm and Araújo has seen that: we have spoken about it and the case is close,” Jules Koundé said. “We have to turn the page, make sure that the anger, frustration and impotence of the other day is used in a favour; in front of us is a strong Real Madrid, given a morale boost by the week that’s just gone,” Xavi said, while Gündogan insisted they had “looked each other in the eye”. The damage, though, was done.