Andres Iniesta has been called many things in his storied career, but "world heritage" was a new one. Then again, the performance that encouraged this eulogy was so good that it was difficult to think of a better alternative.

It was November 21, 2015 – a day that Luis Enrique said would go down in Barcelona folklore. They had just thumped Real Madrid 4-0 at Santiago Bernabeu, with Iniesta scoring a thunderbolt to cap a display that earned him a standing ovation from the home fans.

"He's unique, he's world heritage," the coach said of the Spain star, who had scored in a 4-3 win on Madrid's turf the year before. "He has magic and eyes in the back of his neck.

"This victory is glorious, especially in the way that it came about. This has been a very complete performance. It will go down in history as a memorable game for Barcelona."

It was, arguably, the last truly great Iniesta performance. It was also the zenith of Luis Enrique's Barcelona. This Sunday could see the nadir.

The Catalans drew 0-0 with Juventus on Wednesday to exit the Champions League at the quarter-final stage for the second year in a row. It was the first match in the competition at Camp Nou that Luis Enrique - who will depart at the end of the season - has failed to win and only the third time they have not managed to score in either leg of a knockout tie since the modern format began in 1992.

Either side of that preposterous comeback win over Paris Saint-Germain in the last round, there was a 4-0 loss in Paris and 3-0 defeat in Turin. In the group stage, they went down 3-1 to Manchester City. In LaLiga, Malaga, Deportivo La Coruna and Celta Vigo have all hosted Barca and emerged with three points. Athletic Bilbao won the home leg of the Copa del Rey last-16 tie, too, though they lost on aggregate.

These results are not aberrations; they are milestones on Barca's road to dwindling prowess. They have not turned up in the big away matches this season and there is little widespread belief that this will change when they take to the Bernabeu pitch this weekend.

The decline under Luis Enrique has been steady but irrefutable. Their brilliant treble triumph in his first season saw them win the league with 94 points and beat the reigning champions of England, France, Germany and Italy en route to conquering Europe. 

The Clasico hammering that followed five months later spelled the beginning of the end for Rafael Benitez in the capital. Strangely, it did the same for his counterpart.

Barca won the ball back quickly and got it forward even quicker, allowing Iniesta, Neymar, Luis Suarez and substitute Lionel Messi – returning from a knee injury – to wreak havoc before the opposition could reset their defensive lines. It was a tactic that brought spectacular early success but got the shackles up of fans who hold Johan Cruyff's old possession ways sacrosanct. It was tolerated rather than embraced, as long as results didn't suffer. They did.

Three defeats in a row last term - which included Zinedine Zidane's first Clasico as a coach – left Barca clinging onto the title for dear life. Atletico Madrid dispatched them in two impressive quarter-final matches to end their hopes of making history as the first team to win back-to-back Champions Leagues. A domestic double is never, ever to be sniffed at but the chinks in the armour were clear. This year, they've been exploited.

Those grumblings about style have become full-frontal bellows of anger. Supporters who once watched Xavi and Iniesta pass opponents to death consider it nigh on sacrilegious that two centre-backs, Samuel Umtiti and Gerard Pique, have made the most passes of any Barca player in the Champions League this term. Against Real Sociedad in their last league game, they each completed more than Andre Gomes and Iniesta combined.

Luis Enrique hasn't helped his own cause. He has constantly rotated starting line-ups and formations but rarely used substitutions to his advantage (he made just one in that 3-0 loss to Juve). He has caused friction with Ivan Rakitic and Jordi Alba by dropping them without offering a clear explanation and kept Jeremy Mathieu involved despite the protestations of almost everyone watching.

His frosty relationship with the media has made matters worse. Fans enjoyed Pep Guardiola's passion and the comparative warmth of the late Tito Vilanova, but Lucho's cold and curmudgeonly news conferences have done little to change the perception of a pragmatist who puts results above all else; a Jose Mourinho-type, one might say. There are better things to be in the eyes of a Barca fan.

It's not all his fault, of course. Robert Fernandez's transfer dealings have let the coach down badly. There is even a school of thought that signings have been motivated by politics instead of team performance: Andre Gomes, it has been claimed, was bought because Madrid wanted him; Arda Turan and Aleix Vidal, injured for most of this season, were leverage tools for Josep Maria Bartomeu's presidential election bid. Paco Alcacer has done a serviceable job but he was widely acknowledged as Luis Enrique's fourth choice after Kevin Gameiro, Angel Correa and Nolito said no to being Suarez's understudy.

Regardless of Sunday's result, he will likely end his tenure with a third Copa in three years; even if they lose that final against Alaves, eight trophies in two seasons should never be decried. But if they succumb to another away-day collapse at a critical moment of the season this week, then Lucho's last Clasico will go down in Barca history for all the wrong reasons.