#2 Jeremy Mathieu
Jeremy Mathieu was one of Luis Enrique's first signings and that trust has carried the Frenchman strong till this day. Mathieu has deputised for an injured Gerard Pique or Javier Mascherano in the Barcelona first team but his age, and his lesser influence on the games he's played on this season, could see him leave the Camp Nou this summer.
While Mathieu's experience and poise has helped the team on multiple occasions, even Luis Enrique will recognise the need to reinforce in the summer. His lack of pace on the turn is a huge worry for the Catalans especially since they play such a high line against most teams.
Much like Vermaelen, Mathieu's exit from the first-team will force the team to sign a new defender / promote from the youth. Gerard Pique remains the only senior centre-back who can consistently deliver. Javier Mascherano is a class player but much like the Frenchman, is unable to put in 100% in every game.
Possible replacements: Mats Hummels, Neven Subotic and Marquinhos.