The 1-0 win over Nice last weekend lifted them above Lyon into second and Valbuena has now challenged Marseille to get back into the Champions League.
"It's an important victory [against Nice], but it's not decisive because there are eight matches to come which will also be very important," he told Ligue1.com.
"It's now that we have to stand up and be counted and show that we're a big club that wants that third place. We want to get back into the Champions League, and why not finish second?"
Marseille host Bordeaux on Friday night at 7.30pm.