6 players in that position could leave Barça
Robert Fernández's first summer as first team technical secretary will be hot. Not only because of the temperatures, but also because it seems like he will have a lot on his plate with the potential exits of numerous defenders, as Albert Llimós from the daily Ara pointed out.
On the way out
There are 3 players that are clearly about to leave the club. The one that has probably the most chances is Marc Bartra. The young centre-back did not start a game with Vilanova nor with Martino, and Luis Enrique hasn't still got to consider him as an alternative yet. But Bartra is one of the player that could get the club money.
Adriano is also one of the players that has most opportunities to leave Barça this summer and that could leave some money in the club's cash register. However, for Douglas (more out than in) it is hard to hope for an economic compensation with his transfer: this winter there was no team interested unless Barça took on the full price of the transfer.
It is possible to see them leave
There are also 2 centre-backs who don't have the guarantee of continuity, although it's not that clear they could leave. Mathieu and Vermaelen's appearances show that they're part of the second team as for the coach's preferences and that could bring them out. The Belgian still has good contacts in England and, if Luis Enrique agrees, that could be the centre-back's next destination.
Aleix Vidal's presence in the squad (alongside Sergi Roberto's versatility) may lead Dani Alves, a player with a high wage, to be transferred to lighten the salary charge and the club's expenses. If a destination is found, the Brazilian exit could compensate for the weight of Sergio Busquets and Neymar's renewals.
Even if all of those players leave, Barça will be able to keep a very competitive starting defence without problems: Aleix Vidal, Piqué, Mascherano and Jordi Alba will remain in the basic defence structure.
Llimós explains that Barça want to take in, as a minimum, two players next summer. One we already know: a fourth forward, although Llimós indicates it will hard for it to be Nolito. The other, evidently given the list of potential injuries: un centre-back.
But if in the end the majority of defenders leave, the club would have to extend the incoming transfer list. Luis Enrique likes large squads, beween 23 and 25 players, and various players could be added to the project, like Denis Suárez.