"They are definitely the toughest opponents we've had in a qualifier," said Carragher.
"I know people expect us to get through, but it's not as if we're playing a Mickey Mouse team.
"The Belgian league has a lot of quality and their champions are used to getting into the group stages.
"We had a tough match against Anderlecht a few years ago so I'm not surprised Liege caused us problems.
"They caught us a bit cold in the first leg. Their manager said we were sleeping but they deserve credit for the way they played.
"They were spot on tactically, hitting us on the counter-attack and trying to make us play like a home side. You have to remember they'd gone something like 30 games unbeaten in their own league - and they are a club with European pedigree.
"We didn't play well and we know we'll have to improve at Anfield. Everyone knows how important it is for our season to get into the group stage.
"It's always a funny time for us to have such a massive game before we've got going in the season. Some of our results have reflected that.
"We lost at home to AK Graz in the year we won the competition and had a narrow win in the last minute against Maccabi Haifa two years ago, so anyone thinking we'll win comfortably knows that's very dangerous.
"You have to bear in mind this is probably the biggest game of the season already, and in some cases it may be the most important match they've ever had in their career.
"That makes them very tough opponents so we will have to be on our guard. Any side which can keep Fernando Torres and Robbie Keane as quiet as they did in the first leg has quality. We didn't have any chances in the game.
"It would be unthinkable for us not to be in the Champions League. You just want to get this qualifier out the way, put Europe on the back-burner for a while and get focused for a couple of months on doing well in the league.
"As players we expect to be there and so do the fans. We know in this situation all the pressure is on us, but we don't want to get negative about that.
"All the hard work finishing in the top four last season was geared towards reaching the group stages, so there's no way we want to let that slip.
"If we go through it gives us a bit of momentum and confidence and gives us those six group games to look forward setting up our season."