A win at Signal Iduna Park would secure the Serie A side's place in the knockout stages of the UEFA Champions League from Group F.
Benitez was welcoming of the tough test but said his team needed to be near their best to take anything away from Germany.
"We are facing top-class opponents. We respect them a lot because they have earned it through all the things they have achieved of late on the pitch in the last few years," the Spaniard said on Monday.
"But I like to play these kinds of matches against strong teams because in this way we can show our improvements and we can keep doing things better and better.
"I think that playing against such an opponent in such a vital game for them in the Champions League is always going to be very difficult in any case.
"As Pepe Reina said before, we'll have to be almost perfect against Dortmund."
A draw would be a tremendous result for Napoli, who face group leaders Arsenal on the sixth matchday.
But goalkeeper Pepe Reina urged his side to aim for victory and said it would be dangerous for them to play for a draw.
"We all know what we have to do. The first thing we need to do is playing with a lot of intensity," the 31-year-old said.
"We don't have to think about getting just a draw, otherwise we'll be in fear of losing and this is not good. We respect Borussia a lot because they are a wonderful team.
"We'll have to be good enough to play with a lot of intensity from the start - in this way, things would definitely be easier."
