Right-back - Sergi Roberto
Sergi Roberto is a product of Barcelona's famed La Masia academy. Barcelona fans are usually proud of academy graduates who become first-team members. However, it is clear that Roberto does not enjoy a good reputation among the club's fans.
Many believe that the 29-year-old is not of the requisite quality for Barcelona. This is despite the versatile player making more than 300 appearances in all competitions for the club.
Roberto began his career as a midfielder, but in recent seasons he has become the club's first-choice right-back. The Spain international is in talks with Barcelona over a new contract and is one of the captains at the club.
Centre-back - Gerard Pique
In his prime, Gerard Pique was regarded as one of the best centre-backs in world football. It can be argued that he continues to be the best centre-back at Barcelona.
The 34-year-old is a product of La Masia, but joined Manchester United in 2004. He returned to Barcelona in 2008, and has been an integral part of the club's defense since then. A ball-playing, physically dominant centre-back, Pique is a charismatic player who is Barcelona through and through.
The Spain international scored Barcelona's only goal as they beat Dynamo Kyiv in the group stage of the Champions League a few days ago. Pique in recent years has attracted attention for his business activities, and many regard him as a future Barcelona president.
Centre-back - Eric Garcia
Eric Garcia did not play against Dynamo Kyiv in the Champions League due to a suspension, with the much-maligned Clement Lenglet taking his place.
Garcia should be back for El Clasico, though. Like Pique and Roberto, Garcia is a La Masia graduate. After four years with Manchester City, the centre-back rejoined Barcelona this summer on a free transfer. A highly-rated player, Garcia is already a regular for Luis Enrique's Spain.
The 20-year-old is still in development, and playing alongside Pique should help his cause. Garcia is a technically gifted centre-back who oozes calmness and composure and is seen as the ideal Pique replacement.
Left-back - Alejandro Balde
With Jordi Alba unlikely to play against Real Madrid, youngster Alejandro Balde looks set to start for Barcelona in one of their most important games of the season.
Balde's potential inclusion means that Barcelona will likely field a backline of La Masia graduates. The 18-year-old has been earmarked as a player with high potential. He was one of the main reasons Barcelona decided to sell Junior Firpo this summer.
Barcelona's current environment is not ideal for any youngster to develop in with their financial problems. However, if Balde flourishes during such a difficult time for the club, the Spain U19 international will be adored by the club's fans.
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