The 25-year-old's current deal with the Catalan giants runs out in 2016, and the Argentina international has consistently expressed his desire to remain at Camp Nou.
"We have not talked about contractual issues with Messi," said Zubizarreta. "When the time comes, we will talk but not in public."
Barca vice-president Josep Maria Bartomeu was more positive about Messi's long-term future with the Blaugrana.
"I don't know a single person of Barcelona, member or fan, who doesn't want to see Lionel Messi ending his career wearing this shirt," he said.
Messi, who scored 50 goals in La Liga last season, has found the target four times in three league matches so far this campaign.