The South American outfit are the favourites to claim the trophy on their own patch this summer, but their performances in Group A thus far have been under-par.
Marcelo, however, is still confident that his team have what it takes to win the competition.
"Worried is not the word," he told reporters at a press conference.
"We are aware of our responsibility and every day the Cup gets more difficult.
"Every match is more difficult than the previous one, but still, I think we played better in the second match than in the first."
Brazil face Cameroon in their final group match on Monday.