Barcelona are still working to secure the signing of a much-needed center-back. A deficiency in the center of the Catalan giants’ defense has been apparent for several seasons and has been exacerbated by the retirement of club stalwart Carles Puyol. Given that the club currently has a, for the time being, suspended transfer ban hanging over their heads, it is an issue that unquestionably now needs to be addressed.

It is Valencia’s Jeremy Mathieu who currently appears to be Barcelona’s main target, but the two clubs appear to have reached an impasse. The 30-year-old has already been the subject of a bid from Barcelona, but Valencia are adamant that they will not sell for less than his €20 million release clause, according to reports in Spain. Mathieu, though, has released a statement outlining his desire to make the transfer and urging Valencia to negotiate.

"I am not hiding the fact that this would be a step forward in my career; it is a reward for my hard work and efforts and is a unique opportunity that any player would jump at,” he said, according to Marca.

"I ask Valencia and their president, Amadeo Salvo, to understand my situation and negotiate a deal. I have the chance to play for the biggest club in the world and that's all I want right now, though I will never forget everything Valencia have done for me.

"When I renewed my contract at Valencia last season, the president promised he would let me leave if a good offer came in for me, which is the case now.”

Whether Mathieu would be the only defensive signing remains to be seen. Barcelona are, though, said to be considering other targets. Catalonia-based publication Mundo Deportivo believes Daley Blind features most prominently among those. Blind started every game for the Netherlands en route to their third place at this summer’s World Cup and particularly impressed in the 5-1 demolition of Spain, when providing two assists. In that opening game, the 24-year-old from Ajax started at left wing-back, but he went onto play as a defensive midfielder and as a left-sided center-back during the tournament in an illustration of his versatility.

Still, even for a team that has featured some unorthodox center-backs in recent seasons, it would be a major gamble to target Blind with a view to fielding him in the center of a back four. Blind is arguably best in defensive midfield, where his lack of athleticism is less exposed.  The son of former Ajax legend Danny Blind has also been linked to Manchester United, managed by the Netherlands’ coach at the World Cup, Louis van Gaal.

Another name mentioned by Mundo Deportivo as a possible transfer target is Mats Hummels. The Borussia Dortmund star has been repeatedly linked with a move to the Camp Nou in recent times and further enhanced his reputation as a key part of the Germany side that lifted the World Cup in Brazil. Having already lost striker Robert Lewandowski to Bayern Munich, Dortmund will sternly resist the 25-year-old’s departure.

If reports are to be believed, Barcelona are firmly targeting a left-footed defender, with Jan Vertonghen completing the theme. According to Spanish publication AS, Barcelona have conceded that Manchester United are better placed to secure Hummels and are instead turning their attentions to Tottenham’s Belgium international, who has also played at left-back. Reports in Britain suggest that Tottenham will be far from willing sellers.