The Catalan giants top the embryonic Liga table after two matches in a bright start to Luis Enrique's tenure.
But the 25-year-old De Marcos believes Bilbao – who reached the UEFA Champions League group stages after beating Napoli in a play-off – can upset the new Barcelona coach.
De Marcos said: "We are confident of getting a result at such a difficult place as the Camp Nou and to win against a team of Barca's standing would be even better.
"I think we are increasingly confident in ourselves and we go into every match to win it, but we have taken points from some very important games and will try to do that there.
"Last year we had to go to the Santiago Bernabeu in the third fixture and you've got to play the best teams sooner or later.
"You never know when the best time is but what we do know is that this Saturday is the only thing we are focused on.
"Barcelona demand a lot of you. If things go well it is because the team is playing well. If not we have to correct things for the next games, which are also important."
Bilbao began their Liga campaign with a 1-0 loss at Malaga but bounced back to record a 3-0 home success against Levante.
