They are the reigning European champions, and soon enough they will be Spanish champions too. They are facing Bayern Munich in the Champions League quarter-final tomorrow, hunting for their third European Cup in four years. So why is everyone still wondering whether Real Madrid are any good?

The team who walks out in white at the Allianz Arena on Wednesday could fairly claim to be the best in the world, led by the second and third most expensive footballers of all time. But they do not play like it, they have not been all season and that is unlikely to change tomorrow. Given how much they want to entertain they do not do it very often.

On Friday Zinedine Zidane surprised journalists at his press conference by floating the possibility that he could be sacked by Florentino Perez this summer. “I've one more year left,” Zidane said. “But I am not sure, so I am not preparing anything [for next season]. I am thinking just about what I have left this season. I am ready for everything.”

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No-one expected him to say that at the time but of course it is true. Zidane understands better than anyone the forces that shape this club: the endless search for glamour, for buzz, for ilusión, all embodied in the ambitious capricious president Florentino Perez.

Zidane was a galactico himself once, so he knows how it works. Perez signs the most exciting players he can find for huge fees. Those players then play for Real Madrid. If for any reason the manager does not pick them, Perez can replace him with someone who will.

That, in short, has been the problem this season. Perez is attached to the ‘BBC’, the front-line he has spent more than €200m building over the last few years. The BBC have been very successful for Real Madrid, delivering the 2014 and 2016 Champions Leagues, both against Atletico Madrid, both in dramatic circumstances. You could not ask for much more than that.

But Cristiano Ronaldo has clearly peaked as a footballer, now at 32 years old and after an unprecedented 10-year purple patch. He can do plenty of things well, but not everything anymore. Karim Benzema is not in good form and has only scored nine league goals this season despite being first-choice centre forward. Gareth Bale, who should be at his peak now at 27, has not been the same player after missing three months with an ankle injury.

And yet the BBC continue to start in a 4-3-3 Zidane has built to provide a platform for them. With none of them playing well, Real Madrid look top-heavy and unbalanced, with the midfield and defence too exposed. Luka Modric, their most important player, is in a dip himself and suddenly the whole unit stops functioning.

There is public and press clamour for Zidane to drop his misfiring stars and replace them with more popular Spanish players, specifically Isco and Alvaro Morata. Real Madrid have probably played their best football this season in a 4-4-2, rather than 4-3-3. Morata has more league goals than Benzema in fewer games. Isco is playing better than Bale and certainly brings more balance to the team.

Zidane knows that dropping the BBC would risk him losing his job. Rafa Benitez did not help himself by not picking €80m man James Rodriguez back in 2015, although James has done little since to prove that Benitez was wrong.

So Zidane has little option but to stick with this Madrid team. Yes, their results are good, with one loss in their last 16 games after a mid-January wobble. But it is not the dazzling expansive football that all this money was meant to bring. In fact, they have more set-piece goals than anyone else in Spain so far this season, 25. According to Opta they lead La Liga in goals from corners and indirect free-kicks, with nine from each.

Tomorrow Zidane will face a man, Carlo Ancelotti, just as familiar with the egos, pressures and politics that make Real Madrid such an impossible job. More importantly, this is still more or less Ancelotti’s team from his two-year spell at the Bernabeu. He knows these players’ strengths and weaknesses and now possesses a machine at Bayern Munich that is more coherent and cohesive, and more able to do them damage.

The 'BBC' have led Real Madrid to two Champions League titles (Getty)

Everything is set up for Bayern to give Real a nasty surprise tomorrow. No team has defended the European Cup successfully since Milan in 1990, and this Madrid team is less convincing than most European champions since then. But the great trick of this team is somehow to be overrated and underrated at the same time. It is a mess of individual brilliance which is nowhere near as good as it should be. And yet it has won two Champions Leagues out of three.