Barcelona's end to the year on LaLiga has been so cataclysmically bad that it would be harsh to point to one single reason for their tragicomic vulnerability. But any attempt to define why Barcelona have suddenly become the weak man of Spanish football without naming Robert Lewandowski would be miles off the mark.
The Polish striker has become a glaring and probably unsolvable problem for the Catalan club, and he represents an enormous Achilles heel from which neither of their two main title rivals, Real Madrid and Atlético Madrid, suffer.