The Roma midfielder helped the Italians get off to a winning start against England in Group D but they now face a dangerous Costa Rica outfit which also took maximum points in its opener.
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The Central American side came from a goal down to shock Uruguay 3-1 last week and De Rossi is keen to ensure Italy treats Jorge Luis Pinto’s side with respect as the team looks to all but confirm its own last-16 spot.
"We should fear them a bit. You need a healthy fear against a team that surprised everyone with their victory over Uruguay," he said. "Nobody thought they would get such a clear result against a very strong side.
"They'll be fired up after that win. If they had lost 4-0 then we could've underestimated them, but in this case we cannot possibly do that. I hope, and am convinced, that we can virtually secure qualification by beating Costa Rica. A victory would put a strong stamp on our ticket to the next round."
Italy is hoping to welcome back captain Gianluigi Buffon from injury for the match, while De Rossi himself should be fully fit after sitting out of training with a neck problem.