Victor Valdes and Carles Puyol will both leave Camp Nou at the end of the season - the latter announcing his exit plans this week - and replacing the duo is head coach Martino's top priority.
Borussia Monchengladbach goalkeeper Marc-Andre ter Stegen has been linked with a move to Barca, but Martino insists he has not discussed any targets with sporting director Andoni Zubizarreta.
"I have not met with Zubizarreta or the president, but we do talk regularly," he said.
"What is clear is that, now Puyol leaves, we'll need to sign a centre-back.
"Puyol is one of those players you can't replace, he has left a mark at this club.
"They (Puyol and Valdes) are those irreplaceable players, and it (them leaving) happens to a club from time to time."
Martino also insists that Lionel Messi being sick on the pitch during Argentina's midweek friendly with Romania is nothing to worry about.
"I thought it was the result of flu," he added. "But it is something that he has for quite some time.
"I'm not a gastroenterologist, but do not give it importance.
"It's not normal, but it does not affect the development of his work."
