Both the Spanish giants reached the semi-finals of Europe's premier club competition in 2011-12.
"Two clubs stand out - Barcelona and Real Madrid," he told La Gazzetta dello Sport.
"Barcelona are strong even without [Pep] Guardiola in charge, but they seem less aggressive and slightly less focused in defence now.
"They look more vulnerable than in previous seasons."
"Zenit, coached by [Luciano] Spalletti, and Manchester City, coached by [Roberto] Mancini could surprise people, even though City have been drawn in a tough group, with Real Madrid," said the Italian.
PSG have been drawn against Dinamo Zagreb, Dynamo Kiev and Porto in Group A in the Champions League.