Vermaelen completed his move to Barca on Sunday, signing a five-year contract at the Nou Camp after joining from Arsenal for a fee that could eventually rise to 18.8million euros (B£15million).
The Belgium international joins Luis Suarez, Ivan Rakitic, Claudio Bravo, Marc-Andre ter Stegen and Jeremy Mathieu as newcomers at Barca, who will be under the guidance of new coach Luis Enrique next season as they look to recover from a hugely disappointing campaign under Gerardo Martino.
Speaking at Vermaelen's presentation, Zubizarreta admitted he was very happy with the talent Barca now have at their disposal, but also revealed that the club were still open to more additions if the right players become available.
He said: "With the addition of Thomas we completed a defensive line of a very high level. There are options that we are working on for the exit of some player, as such we're not discarding that others could come in.
"What I can say is that at midnight on August 31 we hope to have the best squad possible. Even though we are very happy with the players that we have, if there is a chance to improve it, we will try.
"Until the first or second (of September), when we talk about the market being closed, anything could happen."
Zubizarreta preferred not to talk about specific targets, which reportedly still include Fiorentina's Colombia star Juan Cuadrado, while he also said Barca had not received any offers for their full-back Dani Alves.
Vermaelen was not short of suitors as it became increasingly clear his future lied away from Arsenal, with Manchester United one of the clubs heavily linked with services, but the 28-year-old insisted it was a "dream" for him to move to the Nou Camp.
"I'm very happy. It's a dream for many players to be here, and I've achieved it. I will play with the best, I will train with them every day and I hope to improve. I will try and adapt as soon as possible," he told a press conference.
"It's one of the biggest clubs in the world, it's a dream, as I already said. Therefore, for a player like me it wasn't a difficult decision to come here."
Vermaelen, who Barca hope will help fill the sizeable gap in defence left by the retired Carles Puyol, struggled with injuries at Arsenal but the former Ajax man hopes his fitness problems are now behind him.
He made only 13 starts in all competitions and 21 appearances in total for Arsenal last season, which concluded with him being an unused substitute in the Gunners' FA Cup final victory over Hull as they collected their first trophy in nine years.
"Last year was a little tough with all the injuries I suffered. I think that happens now and again during a player's career. It could be a coincidence that they all happened in a short period of time," he said.
"The only thing I want is to look to the future, regain my form and fitness. My aim is to play in lots of games and help the team.
"I want to start from zero and I am sure I'll have a fantastic season here at Barca."
Vermaelen's buy-out clause in his contract with Barca is 80million euros (B£64million) and he will wear the number 23 shirt with the Blaugrana.
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