The Partenopei will take on the Liga outfit for a place in the Champions League group stage and their coach accepts they will meet a formidable opponent
Napoli were seeded in Friday's draw and could have drawn Lille, Copenhagen, Standard Liege or Besiktas, but will face the side which finished fourth in La Liga last season.
The Serie A giants were drawn at home in the first leg of the play-off tie later this month and Benitez knows Napoli must perform at the San Paolo to give them a chance of qualifying for the group stages ahead of a daunting trip to the San Mames.
"We were paired with the most difficult side of the five we could have faced, Athletic are the strongest of them all, no doubt about that," he said after the draw.
"They play good football and the great support of the 50,000 fans at the San Mames makes them difficult to beat for anybody.
"I think we will see two beautiful games, played with great intensity by both sides. I think Napoli are well prepared to play a great game and reach our objective, which is playing in the group stage."
Napoli host Bilbao in the week commencing August 18 with the return leg in Spain a week later in what will be the first time the teams have faced each other in competitive action.