Lula -- a founder of the leftist Workers' Party who won worldwide fame for his anti-poverty programs during his 2003-2010 presidency -- is suspected of engaging in influence peddling after leaving office.
However, the Lula Institute said in a statement that he had denied any wrongdoing during a voluntary meeting with prosecutors in the capital Brasilia.
Lula "underlined having never interfered in a contract between the BNDES (Brazilian state development bank) and private companies... nor in the bank's decisions on granting loans," the statement said.
"I always tried to expand opportunities for promoting these companies abroad with the goal of creating jobs in Brazil," Lula said. "Presidents and ex-presidents around the world support their country's businesses abroad."
Lula testified three months after prosecutors opened an investigation that is separate to a huge probe into corruption centered on the state oil company Petrobras.
In particular officials are looking at Lula's relationship between 2011 and 2014 with construction giant Odebrecht, a major builder in projects abroad, but also one of the chief players in the Petrobras embezzlement scandal.