1 Over-reliance on Messi
At the end of the second leg against Paris St-Germain, Barcelona's players heralded Leo Messi as "irreplaceable". Even "half crippled", he had changed the game. It said something about their dependency on him that the rest of the side had, in David Villa's words, been transformed with his mere presence. It is a dependency that is growing and, while Messi makes a strong claim to be the best player in history, it has affected those around him, reducing them to supporting roles. Against Bayern, the flaws in that approach were laid bare. Leo Messi simply was not fit. He never escaped the defence, completed just two of 14 attempted dribbles and did not provide a single telling pass. If he had saved them before, he could not here. If he couldn't, who could?
2 The Alex Song transfer
Even at the time, it was hard to make sense of it. Back in the summer, it was clear that Barcelona needed to buy a central defender – but they did not. Instead, Alex Song arrived. In fairness, Barcelona had been priced out of the market on both Javi Martínez and Thiago Silva but even then it was a questionable signing. Barcelona suggested that he was a two-in-one, a player who could play in the middle of the defence and also provide cover for Sergio Busquets. A bit like Javier Mascherano, in other words (or like Martínez). The experiment at the back failed and was quietly dropped, but nor was Song used as cover for Busquets when it really mattered. Against Bayern Munich, Busquets was clearly struggling. Here was a game where Song might have been useful. But Vilanova decided against using him. Nor did he use Cesc Fábregas, who may yet have a role as Xavi's replacement but whose performances on his return to the Camp Nou has been decidedly uneven. His best position is as the false No9 or off the striker ... and a certain Leo Messi plays there. Barcelona have a short squad and rotate rarely. Even those that they could use were not used.
3 Vulnerable defence
Barcelona's "vulnerable" defence is something that has been talked about for a long time. Often it was a bit of a myth: Barcelona chose to take the risks that are implicit in playing with a high defensive line because they considered that the benefits outweighed the disadvantages. Yes, they left space behind but the system prevented the other side from getting the ball. At least it did for as long as there was high intensity and pressing – and that has largely been absent recently. Then there are the basics: height, aggression, strength, competitiveness, concentration. Rarely has a team looked so consistently vulnerable from set plays. Bayern Munich dominated Barcelona but two of their goals came from corners.
4 Injury problems
There is no escaping the fact that physically Barcelona have struggled. Every season, they have a dip around February. The difference is that most seasons they come out of it; this time they did not. There's none of the speed and intensity that used to define them. That's partly tactical, partly physical. And that fatigue has been joined by injury. Busquets and Messi were both in far from perfect shape. Worse, a whole raft of injuries hit in the same place. That's a factor that needs to be thrown into the equation when it comes to defensive criticisms and the question marks over Barcelona's signing: if Carles Puyol and Gerard Piqué are fit, there is not really a free space at centre-back. Mascherano, Puyol and Adriano, a convert, were all absent.
5 Shadow of illness
Managers are fond of talking about how their side overcame adversity. Normally, it's meaningless; in Barcelona's case, it's actually true. Eric Abidal and Tito Vilanova have both undergone treatment for cancer. Abidal is now playing again: doctors say it is a miracle that he is healthy, let alone competing once more. Vilanova, Barcelona's coach, was diagnosed with a relapse of his cancer and went to the US for treatment. Emotionally, that has a huge impact. In purely footballing terms it does too. Barcelona were effectively without a coach and we don't really know just how well Vilanova is now. In those circumstances, it would be strange if there was not an impact on the team.