Liverpool manager Rafael Benitez is wary of the threat posed by Benfica having previously been dumped out of Europe by them.
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Four years ago the Portuguese side ended the Reds' hopes of becoming the first side to win back-to-back Champions League titles when they lost 3-0 over two legs.
Benfica are currently three points clear of Braga at the top of the Portuguese Liga and Benitez will not underestimate their last-eight opponents, who include among their ranks Pablo Aimar, who Benitez managed at Valencia.
"We know they are a good team and, of course, we have played them before in the Champions League," said the Liverpool manager. "They are a massive club with a lot of support from their fans and it will be a tough game.
"They are top of the table and playing really well at the moment. I know a number of their players well - Aimar, Javier Saviola, Javi Garcia - so we know they have a lot of quality."
Benitez has got his preferred order in terms of the away leg being first but he is concerned the Anfield factor may not have as much of an effect on Benfica as it has had on other visiting sides over recent years.
The Lisbon side won 2-0 on Merseyside back in 2006 and the Liverpool boss believes that will give their opponents confidence.
"It's always important that the second leg is at home in front of our fans," he added. "We know we have to perform away and then play well at home. We have the confidence to do that and are looking forward to the games.
"Because we have played Benfica before they will know Anfield and so may not be as scared as other teams, but we have to do things properly and try to go through."
Liverpool defender Daniel Agger insists the players fully believe they can win the Europa League and are not worried by any side.
"This is the last trophy we can win so we have to give everything we can to win it," said the Denmark international. "We have to show it on the pitch and I think we did against Lille.
"If you have to win a tournament like this one you should beat them all."
Midfielder Javier Mascherano echoed Agger's comments, saying: "All the teams in there have showed why they are at this stage. Any team from now until the end will be difficult. If we want to be in the final we need to continue improving and try to take another step up."
