The Barcelona sporting director says the Brazil international could have cost €100 million, rather than the €57m his club paid for his services
The Brazil international became the ninth most expensive player of all time following his move from Santos in May.
However, the former goalkeeper has insisted that he could have cost the club a world record fee of over €100m.
"A purchase of €57m is extraordinary," Zubizarreta told reporters. "[But] I look at the overall buy and the expectations of the business.
"If the expectation was of nearly €100m and we have paid €57m, it is an extraordinary buy."
The former Spain goalkeeper was also asked whether he thought his club's sale of 22-year-old Thiago Alcantara to Bayern Munich, for a fee which could rise to €25m, represented good or bad business.
"I do not approach it as business, he wanted to evolve as a professional," said the 51-year-old. "We received €22m, with two variables that Bayern will pay us as well and €1m more from a friendly.
"We've got €25m, that's what I know. It is good under the circumstances," he added.