In Sergio Ramos, Real Madrid can expect to find a leader and embodiment of Madridismo and one who is capable of contributing both defensively and offensively. At the back the Spanish international has been impressive this season as he boast more interceptions and blocks per game in La Liga than any other player in the squad. Unsurprisingly he also concedes more fouls per game than any other player in the squad.
When fit and mentally focused he is the best central defender in the world. The problem is that Ramos is not always concentrated to the level that he is capable of and therefore we occasionally see some sloppy goals conceded due to a lack of proper communication or organisation. Thankfully though, he usually rises to the occasion and plays well on the big stage.
As always a big question is whom should partner Ramos in central defence. In previous seasons however, that question may have been harder to find an answer to. Whilst Raphael Varane has steadily improved through the second half of this season, there is no doubt that Pepe has been Real Madrid's most consistent centre back this season and deserves to start another Clásico due to his performances.
Moreover, one aspect of Pepe's game that has been particularly impressive has been his willingness to temper his natural aggression and it has produced dividends on the pitch. He averages less than a foul per game in La Liga which is astonishing considering the reputation he carries. In addition to his new found cool-headedness, Pepe averages the 2nd most interceptions and 3rd most clearances per game in La Liga from the Real Madrid squad. Let us not forget that Pepe also scored the critical second goal in the reverse fixture last October and his aerial ability is sure to help Madrid.
At right back you can expect to see Dani Carvajal who has played to an excellent standard so far this season. Unfortunately age has caught up to veteran Álvaro Arbeloa and has been a limiting factor in his ability to deal with pace - of which there shall be plenty in the likes of Neymar, Lionel Messi and Luis Suárez. Therefore Madrid fans should hope to be able to count on Carvajal to provide the right balance of offence and defence in order to keep the Barcelona attack honest. Bear in mind, it was something he was unable to do in the last Clásico as Neymar scored after only 3 minutes.
At the beginning of the season Carvajal was visibly playing with anger and whilst some pundits voiced concerns about his level of aggression perhaps that is the sort of intensity and fire the Madridistas need to see from the team once again. Certainly, when it comes to the technical, defensive side of the game Carvajal has been superb. He averages 3 successful tackles per game in La Liga which is more than any other player in the squad.
Left back is not a debate at the moment as the rejuvenated Marcelo has been a shining light for Madrid along the left flank all season long and there is an argument to be made that he has been the most consistent performer on Madrid's left side. His piercing runs have often given Los Blancos the outlet they need when Cristiano Ronaldo has not been in his best form since the turn of the year. Furthermore, the only defender who completes more successful tackles per game than him in La Liga is the aforementioned Dani Carvajal.
Fabio Coentrao can count himself slightly unlucky as injuries once again derailed his chance at a secure starting position. Many should recall that the Portugese was fantastic at the tail end of last season, especially in his assists to the Bale goal in the Copa del Rey final and Benzema's winner against Bayern Munich in the Champions League semi-final first leg. Unfortunately for him, Marcelo has recovered the form that made him so formidable between 2010-12 and rightly the Brazilian will take his place in the starting XI come Sunday.
Switching over to Barcelona now. In central defence one can expect to see their summer signing Jeremy Mathieu ply his trade. He has been very solid for the Catalan's and has averaged more interceptions per game in La Liga than any other player in the squad. He couples experience with a fast turn of pace over the first 10 yards and therefore seems apt to deal with Madrid's forwards. Of the established central defenders, only Gerard Piqué has played more minutes than him.
Which moves us on to Piqué himself. In my opinion he has recovered some - not all - of the form that saw him become lauded as one of the very best centre backs in the world when he was winning the World Cup with Carles Puyol. He averages more clearances and blocks than any other player in the squad which points to his improvement in his defensive positioning this season. Many in the Spanish media tried to point the finger at Luis Enrique's tactics whilst Real Madrid were on their 22-match winning streak yet it is he who has most likely been the reason behind Piqué's improvement.
Barcelona will desperately need Piqué if they are to compete with Real Madrid in the air. From set-pieces and corners too, the 6' 4" Spaniard will be key to both defending and attacking the ball against the likes of Sergio Ramos and Pepe. Furthermore, he is actually Barcelona's fifth highest scorer in La Liga this season chipping in with four goals so he certainly shouldn't be overlooked.
The young, talented Marc Bartra could well play but I'd reckon that it's more probable that he's to play in Barca's midweek Champions League home fixture against Manchester City. Whilst Javier Mascherano, who often plays as a centre-back for Barcelona is likely to fill in at his more natural role of defensive midfielder as a replacement for the injured Sergio Busquets.
Despite visibly regressing over the past couple of seasons, it wouldn't be silly to expect to see Dani Alves start El Clásico in Barcelona's defence as the Brazilian has little competition from the likes of Martín Montoya and fellow countryman Douglas. He averages more tackles per game in La Liga than any other player in the squad and that may well be the reason why Barcelona are preparing to offer him a new contract this summer, according to Mundo Deportivo.
Offensively Alves has lost some of his former spark, no doubt. He has registered a couple of assists this season but one often hears the Barcelona faithful bemoaning his inaccurate crosses from promising positions and if his poor deliveries continue then I'm certain that Carlo Ancelotti and co. would be most grateful. Crisitano Ronaldo should certainly look to exploit the space that Alves leaves behind him when he does join the attack. Quick transitions could be beneficial to Real Madrid if they recover the ball but with the more possession orientated system Ancelotti enjoys may well hinder the chances of implementing such a tactic.
Jordi Alba is the undisputed starter at the left-back position for Barcelona. His level too, like Alves, seems to have dipped over the past season or so but not to the same extent. The former Valencia player is always capable of torturing opposition defences with his blistering and relentless runs down the wings. Once again, like Alves, Alba has shown over the years that he is very capable of leaving space in behind him though and if Gareth Bale can continue the form he showed against Levante then perhaps Alba will be more hesitant in bursting forwards.
Only Lionel Messi and Claudio Bravo have played more minutes than Alba this season in La Liga and it is a testament to his consistent quality that in a season of much turbulence and experimentation at Barcelona that Luis Enrique continues to choose him time and again. Certainly the battle between himself and compatriot Dani Carvajal on the right side of the pitch shall be more than interesting to spectate.
In conclusion, whilst Barcelona have defended better as a unit than Real Madrid over the course of this La Liga season, I still believe their defence contains some fundamental deficiencies, such as the space left in behind them, that can be exposed more easily than those of Madrid. If anything, this was evidenced in the reverse fixture for Madrid's third goal when Karim Benzema stroked home to hammer the final nail in Barcelona's coffin on that particular day. Much of the match will also depend on whether Sergio Ramos and his fellow defenders show the correct level of concentration and organisation to step up to the grand stage that is El Clásico. That said, if I had to choose which team had better individual defenders, I would go with Real Madrid's over Barcelona's.
Advantage in defence? Real Madrid.