Napoli host Luis Castro's men trailing 1-0 from the first leg at the Estadio do Dragao.
However, the Italian outfit have already shown that they can beat talented European opposition at the Stadio San Paolo this season, overcoming Borussia Dortmund and Arsenal at home in the Champions League group stages.
The last two Serie A encounters have seen Napoli claim 1-0 wins against Torino and Roma, who they trail by three points in the race for the final automatic Champions League qualification spot.
And, while Benitez concedes that the league remains Napoli's priority, he is keen for his side to progress in order to aid the development of the team.
"We are confident," he said. "We have shown that we can win at home, we have already done it in the Champions League. San Paolo could be the decisive factor.
"Our primary objective for the rest of the season is second place in Serie A, but at the moment the most important game is tomorrow (Thursday).
"For the development of the team it is important we go through.
"We need to approach the game with the idea of winning, we know if we score a goal we have a bit more time. We must think about scoring the first goal, not the second or third.
"Against Arsenal and Dortmund we played with an intensity that everyone enjoyed.
"In the recent games with Roma and Torino however, we won with our character.
"Our objective is to have a team that continue to create chances to score while at the same time having a more and more solid defence."
