Five things that will decide the Clasico
1. Barcelona's makeshift defence
Javier Mascherano has shown during his two seasons at Camp Nou that he is adept at playing in the centre of defence and, when lining up alongside either Gerard Pique or Carlos Puyol, looks as if he has always been a defender. But the problem for the Argentine is that Pique is a major doubt for the game on Sunday, while Puyol is certainly out after dislocating his left elbow during the Blaugrana's midweek Champions League victory over Barcelona.
Which leaves Alex Song.
The midfielder travelled the well-trodden path from North London to Catalunya this summer, joining Barcelona from Arsenal. Expected to challenge for a starting role in midfield, the Cameroon international has instead found himself playing in defence with Mascherano for much of his six appearances for the club so far this season.
Song is a decent player but a defender he is not and, with Cristiano Ronaldo, Angel Di Maria and Karim Benzema all hitting form in the week building up to the Clasico, Sunday evening could well be a night to forget for Tito Vilanova's auxiliary centre-back pairing.