Benitez's men were indebted to Gonzalo Higuain's second-half equaliser in last week's first leg, the Argentinian cancelling out Iker Muniain's opener as the game in Naples ended 1-1.
That result means Napoli must score at Stadio San Mames if they are to progress to the first-round proper, but Benitez believes Athletic's long wait for Champions League football could weigh heavily on their minds.
"Athletic Bilbao haven't been in the Champions League for 16 years, so tomorrow the entire population will be behind them," he said in a press conference on Tuesday.
"However, that can put extra pressure on Ernesto Valverde's men."
It has been suggested that the success of Napoli's season could hinge on Wednesday's result, but Benitez believes any such talk is wide of the mark.
"Nothing will change in the project, because at the end of the day there are so many elements to it," he said. "Going out would not be a tragedy.
"Maybe Athletic have a small advantage in fitness terms, as they have played more competitive games. What worries me about the match? Nothing, from the psychological aspect to the ability to hold out under pressure.
"We have the right players to do well tomorrow night. Athletic won't just sit back and wait for us, nor play for a 0-0 result. We must focus on scoring a goal."
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