The Barca boss feels that the visitor's daring approach to football means they will come to the Nou Camp looking to win the game.
Guardiola described Osasuna as "a demanding side" in an interview published on the club's website.
"They [Osasuna] come at you," he said.
"We have to play well and quick or the tie will be a difficult one."
However, the last time the two sides met at the Nou Camp it was far from difficult for the Catalans as they ran out 8-0 winners in the league match.
"That was a long time ago, and a result like that will be added motivation for them. The situation has changed. This is an 180 minute match and we have to try to get a good result," he said.
Jose Luis Medilíbar's side are fifth in La Liga and almost unbeatable at El Sadar, their home ground.
"Mendilíbar is ambitious, and that's why his daring team are fifth with 25 points. They'll clearly be coming here looking to win the tie, and by doing that Osasuna will help us get back into competitive football ... we are going to have to attack well and create lots of goalscoring chances," Guardiola said.
Barca will play the winner of Real Madrid's clash with Malaga in the quarter-finals with Jose Mourinho's side winning the home leg 3-2 on Tuesday night.