The two rivals meet in Le Classique at the Parc des Princes this weekend with champions 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 have not lost at home in the league all season, and have only dropped points on three occasions, but Valbuena still believes he and his team-mates side can spring a surprise.
Marseille are currently unbeaten in their last five league matches and according to the 29-year-old midfielder they are desperate to make it six with their first win over PSG since November 2011.
"Paris is the favourite," he told L'Equipe. "It is logical that they are when you consider the difference in the standings.
"Fortunately, favourites 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 them become a side that are 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."
