Despite the "financial superior power" of les Parisiens, the midfielder believes Marseille can emerge victorious against Laurent Blanc's men.
The two rivals meet in Le Classique at the Parc des Princes this weekend with champion PSG five points clear at the top of the table and a further 18 ahead of fifth-placed Marseille with 12 games remaining.
Laurent Blanc's side has not lost at home in the league all season, and has only dropped points on three occasions, but Valbuena still believes he and his teammates can spring a surprise.
Marseille is currently unbeaten in its last five league matches and according to the 29-year-old midfielder it is desperate to make it six with a first win over PSG since November 2011.
"Paris are the favorites," he told L'Equipe. "It is logical that they are when you consider the difference in the standings. Fortunately, favorites do not always win. They are not unbeatable, we have seen recently with Montpellier (in the Coupe de France in January).
"We'll be ambitious, because our goal is to keep our winning streak going in hope of making third place."
Valbuena suggested PSG's new-found financial strength has seen it become a side that is almost too big for Ligue 1, something that leaves him disappointed.
"I would of course rather there was no 18-point gap between us," he added. "But for two years, Paris has changed status with financial power far superior to ours.
"The club attracts big players and formed a team that radiates beyond Ligue 1.
"In addition, this year, it exudes a real collective strength. I'm not Marseilles birth but that does not make me happy to see PSG take precedence over OM."