Liverpool's reinforced squad must build on their ruthless form from last season if they are to challenge defending Premier League champions Manchester City for the title, manager Jurgen Klopp said.

Klopp has made four big money signings, adding goalkeeper Alisson, midfielders Naby Keita and Fabinho and winger Xherdan Shaqiri, giving supporters genuine optimism ahead of the new campaign.

But the German insists they are still underdogs in the battle for the league crown, saying: "We are still Rocky Balboa and not Ivan Drago.

"We have to be more consistent. More clinical. More aggressive in the right moments. We need to improve everything.

"We have to be in a championship mode. We jump into the water and we dive until we don't have oxygen anymore. That's the plan. A lot of people think because of the transfer window we will (challenge more) - but that's not how it is."

Klopp accepts the pressure ahead of Sunday's opening match against a much-changed West Ham United but said his team will also need a change in luck if they are to catch last year's runaway champions City.

"Someone gave me the unluckiest team article," Klopp added, referring to a study released this week that said Liverpool dropped the most points last season, 12, in matches affected by wrongly disallowed goals or incorrect decisions.

"You ask me about the gap with City. We had three points from City and they had three points from us. It's about losing them in other games."

Klopp said there could be further departures from Anfield, with the transfer window still open for major leagues in Spain, France, Italy and Germany.

"The window is only one way closed so we cannot buy any more but we can sell not in Premier League - but it is clear things will happen," he said.