Guardiola decided to end his four-year spell in charge after being eliminated by Chelsea in the Champions League semi-finals, with his assistant Tito Vilanova named as the new coach for next season.
However, Laporta, who promoted Guardiola to first-team boss in 2008, told Canal Plus that Rossell had failed to make the necessary guarantees to try to convince Guardiola to stay.
He said, "One of the consequences of the performance of Sandro Rosell's board is to destroy everything that we did in our era. Therefore, it was inevitable Pep Guardiola would walk away.
"I think they could have done more for him to continue in charge.
"My perception is they didn't do what was necessary because they weren't interested in him staying there."
Zubizarreta says Guardiola's own words prove the current Barca board did everything in their power to keep the man who has so far delivered 13 trophies in his tenure, with the Copa del Rey final still to come later this month.
He told TV3: "I am no-one to answer Laporta, but Pep has already said we did everything possible to try and get him to stay.
"Guardiola informed us of his decision on the Wednesday after the defeat to Chelsea. Afterwards there were many meetings, they were hours that seemed like months, until on the Friday morning Tito told us he would take charge."
Zubizarreta also outlined the club's intention to try and protect Vilanova and indicated the new manager will take on far fewer media responsibilities than his predecessor.
"He will constantly be compared to Guardiola but we have to view things as they are, not how they used to be," he said.
"We will help Tito and protect him as much as we can. He will only be responsible for the footballing side of things because he is different to Pep."
The former Spanish international also denied Dani Alves could be on his way out of the Catalan club and that an agreement had been reached with Valencia for the transfer of Jordi Alba.
"Alves is our player," Zubizarreta said. "We renewed his contract a short time ago, last year he appeared irreplaceable and in principle we have no intention of selling him.
"I can flatly deny that we have reached a preliminary agreement or have met with Jordi Alba.
"If there are two clubs I respect they are Athletic Bilbao and Valencia because that is where I played."
However, Zubizarreta did confirm Martin Montoya, Marc Bartra and Marc Muniesa will all graduate to the first-team squad from the Barca B team for next season.