Valencia are reported to want €20 million for the Frenchman, who at 30 years old would hardly represent a long-term solution to the void left by Carles Puyol's exit but would patch up the defensive gaps somewhat.
With Luis Suarez, Marc-Andre ter Stegen, Claudio Bravo and Ivan Rakitic already in the bag this summer, the club's sporting director stressed than Barca's first priority now is to sign a central defender but conceded that many other top clubs are in the same boat.
"Valencia already know our offer and we want to maintain privacy in the negotiations," Zubizarreta told reporters on Wednesday. "Of course we have other alternatives if this falls through.
"Hopefully by La Liga's start we have that centre-back position covered. If we wanted a centre-back before now, we would have signed one.
"We want someone who can put in top performances for many years and that's what we're working on.
"Signing is a centre-back is an objective for 80-90 per cent of the major European clubs so it not only depends on what we want to do - the exception is David Luiz to Paris Saint-Germain, that's the only real major movement in this regard."