The Andalusians currently hold a five-point advantage over Sporting Gijon and Real Zaragoza in the bottom three, but Resino believes those sides could fare well in the three remaining games.
"At the end of the season there are strange results because the teams behind push strongly and those above relax too much," he told Marca.
"Tomorrow [Tuesday] we need to win to widen the advantage or, in a very worst case scenario, not reduce it."
Resino, though, is wary of Espanyol's pace in attack.
"They are a team with a lot of movement up front, they have good and very quick players" he said.
"They are having a very good season and moreover they still have an objective to achieve."
The hosts will be boosted by the return of Dani Benitez and Ikechukwu Uche after both missed the 3-1 defeat to Levante last time out but Roberto, Pape Diakhate, Fran Rico and Hassan Yebda remain out.
Espanyol boss Mauricio Pochettino, meanwhile, is looking for a reaction from his players after Saturday's 3-0 defeat to Sporting Gijon.
The Catalans have now won only one of their last eight, but even though their European ambitions seem to have all but diminished, Pochettino is still targeting a top-seven finish.
He told the club's website, "It will be an intense match in which they are playing for a lot, but so are we.
"Europe hasn't been ruled out as an objective, but the atmosphere of the past few weeks hasn't been the most suitable to achieve these important things."
Sergio Garcia, Kalu Uche and Christian Gomez are all expected to miss out for the visitors after picking up injuries in the Sporting game, so there could be long-awaited recalls to the starting line-up for Alvaro Vasquez and Vladimir Weiss.