La Blaugrana, who need a win to keep pace with league leaders Real Madrid, are expecting midfielder Andres Iniesta to return to the lineup after suffering a muscle tear before the winter break.
However, Guardiola insists that it will still be a difficult test when the Catalan clubs clash for the first time this season.
"We try to take every game seriously but this is the derby," he told reporters. "There has been many games which makes us know what to expect and what we are going to find.
"If we are not in good shape, we will be in trouble. Espanyol play well and are a team with a similar philosophy to us, even if we do have the greater purchasing power.
"It is certainly a special event during the year."
Meanwhile, Real Madrid will look to extend their lead at the top of La Liga to six points with a win over Granada.