Luis Enrique’s final days at the Camp Nou are dark ones and they could get even darker yet. That is how he sees it, at least – a dystopian vision of his immediate future, a gory goodbye as his time at Barcelona comes to a grisly end. After their superb 3-0 victory over Sevilla on 5 April, hope briefly emerging after an impressive run, the Barcelona coach said that he’d had a great time but insisted that if and when they lost “a cannibal holocaust” would be released.

Three days later, Barcelona were defeated 2-0 at Málaga; three days after that they were beaten 3-0 by Juventus in Turin and eight days after that they were knocked out of the Champions League. Four days on, they visit the Bernabéu, another title perhaps slipping from them. They may not be cannibals but there will be plenty coming for him. Lose and the consequences will be dire. Defeat in Málaga, declared unforgiveable by the local media, meant the league was no longer in their own hands; defeat at Real Madrid would make it virtually impossible.

Some have been coming for Luis Enrique from the start and he survived – but now the end is coming. He has six La Liga games left as manager; the next match will go a long way to deciding how his final season ends and how he is remembered.

Asked recently if he felt that he was going through his worst time at Barcelona, he just scoffed: “Er, no.” In his first season, he had been close to being dismissed in January; five months later he had won the treble. The season after, they won the double. If they do not win on Sunday, the best they can realistically hope for is the Copa del Rey, the least significant of the titles (they face Alavés in the final at the end of the season). Real Madrid would surely win their second league in eight years.

“There was no miracle, but there is still a double,” the headline in El Mundo Deportivo ran on Thursday. There could be, but not if they lose on Sunday. In four days, it could have all gone – four days and 22 minutes in Turin. “I’ll remember that for ever and ever,” Luis Enrique said, the regret plain.

Fans sang their way through the final minutes, which was appreciated, but it also felt as if they were marking the end and there was no escaping reality. At full time, Neymar left in tears and Lionel Messi, beaten, wore a black eye.

“It will be hard to pick them up,” Luis Enrique said after their Champions League elimination, “but we have the best stimulus a Barcelona fan or player can have: playing our greatest rival at the Bernabéu. It will be easy to motivate them.”

Gerard Piqué said: “It will affect us because we’re human but Sunday is another challenge and we will compete and try to win. We’re not in our best moment but we will go there to win.” Luis Enrique packaged it as an opportunity but it is an obligation, too. “We want to win the league – and that depends on winning at the Bernabéu,” Andrés Iniesta said.

Lose and they would be six points and the head-to-head record behind their rivals, who have a game in hand, with five games to play. “What we have to do there is what we have done before,” Iniesta said. Piqué agreed: “The Bernabéu has been good for us.”

That is true – they have won four of their past seven visits in La Liga – but they know it will not be easy. That night against Paris Saint-Germain counsels against ever ruling them out and there is sufficient talent for sure but Wednesday, in Piqué’s words, hurt.

Barcelona is not a team that has fully convinced this season nor, it might be added, are Madrid, and nor is it one whose identify is as steadfast as it once was: the accusation levelled at Luis Enrique, even when they were winning, is that Barcelona are losing their religion. Now they are not winning, either. On Sunday, they absolutely must.

Some have been coming for Luis Enrique from the start and he survived at Barcelona – but now the end is coming. Photograph: Josep Lago/AFP/Getty Images

This is not the team that won 6-2 or 4-0 there. It is not even the team that played on Wednesday either. Neymar is suspended and although Barcelona appealed to the court of arbitration for sport, their chances appear slim. There may be a touch of desperation in the way they have pursued it and with some justification as his probable absence matters enormously. Gareth Bale’s possible absence with a calf injury, by contrast, may not. Isco, Marco Asensio, James Rodríguez and Lucas could all replace him; no one can replace Neymar, still less with Arda Turan out.

This is a season that may not be defined by the players on the pitch so much as by the players on the bench, in fact. Only Messi has a better-goals-per-minute ratio than Álvaro Morata, while Michael Reschke, Bayern Munich’s sporting director, recently told El País that someone should build a statue to the man who signed Asensio. Samuel Umtiti apart, Barcelona’s summer signings have barely made an impact; designed to offer strength in depth, they have been unable to step up. That has been decisive; organisationally, institutionally, Barcelona’s issues run deep.

Even if they were to win another double, there are doubts at Barça. Luis Enrique is going with no manager announced yet – although Ernesto Valverde is favourite to take over. Messi is yet to renew his contract. And Iniesta hinted that he may not continue. It would be easier to go with a title, although not winning one would perhaps sharpen the focus. There is little confidence now. At Madrid, things feel different as they chase a first league and European Cup double in 59 years.

“We have to win every game and hope Madrid slip up,” Sergi Roberto said. But even when Madrid look like they are going to slip up, as they often have, they do not. There is something about them, call it luck, confidence, talent, attitude, variety, whatever you like, but Zinedine Zidane’s team have found ways to win where Barcelona have not. They have picked up 19 points from losing positions, including last week when they twice trailed relegation-threatened Sporting Gijón and eventually won, with Isco scoring in the 90th minute.

Zidane has not lost a clásico but he has been mighty close: those 19 points include the last-minute header Sergio Ramos scored when the biggest rivals in the sport, in any sport, met at the Camp Nou.

So here they are. “If we win, we will put ourselves firmly in the title race,” Luis Enrique said. And if they do not, he knows what awaits or he thinks he does – and his are terrifying thoughts.