Silvio Siriana said, as quoted by ANSA, that Russia had earlier proposed Prodi, also former head of the European Commission, the presidency of South Stream, but that he had not found it possible to accept the job.
"It is highly unlikely that anything will change," Siriana said.
Russian business daily Kommersant said on Monday, citing a government source: "Analysts believe that Gazprom will do exactly as they did with Nord Stream and former German chancellor Gerhard Schroeder, who heads the shareholders' committee." The post is roughly equivalent to board chairman.
Prodi meets with Gazprom and Eni CEOs in Rome on Monday. He is to step down as premier in a few days to give way to media tycoon Silvio Berlusconi, who won Italy's general election in mid-April.
The estimated cost of the South Stream project is $14 billion.