Jurgen Klopp believes Liverpool will have to "kick out a big one" if they advance past Porto in the last-16 of the Champions League.

The first leg of their tie is on Wednesday night in Portugal. The Reds will be attempting to reach the quarter-finals for the first time in nine years.

Liverpool have beaten Porto twice in their last two meetings, with the other games resulting in a draw. But Klopp understands it'll be no easy task seeing off the 2004 Champions League winners.

"They are very experienced," said Klopp. "They're very aggressive, very physical and it will be a heated atmosphere as well, so there's a lot we have to deal with.

"But they haven't played very often against a team like us, so it's a same problem they'll have. They are a football-playing side, they fight like they want to show that they are there and want to go through to the next round.

"They are a big club, a proud club, as we are. It's cool to be in the last 16 but we have to kick out a big one to be in the last eight."