Liverpool s German manager Jurgen Klopp applauds the fans following the English Premier League football match between Brentford and Liverpool at Brentford Community Stadium in London on September 25, 2021. AFP
The six-time European champions started their Champions League campaign with a 3-2 home win against AC Milan in Group B.
Liverpool are top of the Premier League ahead of Monday's match between Crystal Palace and Brighton but they were uncharacteristically sloppy against Brentford at the weekend, twice throwing away the lead.
They had conceded just a single league goal in their first five games.
But Klopp said he had spoken about the issues with his players and was confident they could put things right.
"It's not that much of a concern," he said at his pre-match press conference on Monday. "I don't think you should make these things bigger than they are but we have to show a reaction, that's for sure.
"I think it's really tricky to win a football game when you are not defending on your highest level and that's what we didn't do."
Liverpool have won their past two away matches against the Portuguese side by an aggregate score of 9-1, in 2018 and 2019, but Klopp said those results were meaningless in the context of Tuesday's contest.
"Porto always change a little bit, they've had players going out and coming in, still the same manager," he said.
"But we don't think about the last two games, we think about this game They have different opportunities to set up line-up-wise and system-wise and we have to be prepared for that."
"They are a top side, no doubt about that," added the German manager.
"They qualify year in, year out for the Champions League, they are always first or second in the Portuguese league -- that's a top team -- and that is what we are preparing for, not for a team we beat in the past."
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