Liverpool boss Jurgen Klopp struck a sombre note on Friday after it was confirmed that the club could not finish in the Premier League's top four but said he was optimistic as they rebuild for next season.

Liverpool's hopes of qualifying for the Champions League ended when Manchester United thrashed Chelsea 4-1 on Thursday to guarantee a top-four finish and ensure Klopp's side would end the campaign in fifth place.

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After narrowly missing out on an unprecedented quadruple last season, winning two domestic cups, Liverpool will not feature in the Champions League for the first time under Klopp since his first full season in 2016-17.

Klopp said he was "very self-critical" after they struggled to match the standards they set last season despite a late resurgence that earned them a spot in the second-tier Europa League.

"This has not been a historically good season. We're absolutely not happy with it, we made mistakes and were not consistent enough," Klopp told reporters ahead of their final game of the season, away at Southampton.

"After Dubai since we were in training camp after the World Cup, not everything was great but the amount of points we collected since then is pretty good. If we could have done that all season, we'd be in a different place.

"So of course there are reasons for optimism... The atmosphere our people created in the last home game, the way the club said farewell to the players who are leaving... all of these things are the basis for a fantastic future."

Liverpool forward Mohamed Salah said he was devastated after the club failed to qualify for the Champions League and although Klopp agreed with his Egypt international, he said the squad was still united.

"The dressing room is not in a bad mood, we learned to deal with the situation," Klopp added.

"We didn't get divided in one moment between manager and team which is super helpful, we didn't point fingers at each other -- it's all good.

"If you don't qualify for the Champions League the best possible place you can end up is fifth, so that's what we did. If you'd asked me that 10 games ago I'd have said, 'no.'"

Liverpool will need to strengthen their squad with the departures of key figures such as Roberto Firmino and James Milner in the close season.

When asked if the lack of Champions League football would be a stumbling block in the transfer window, Klopp said: "I don't think so, but we will see.

"It is always possible and probably likely that things won't go as big as you want because the better the player, the less the desire of the other club to let him go.

"We are prepared for that. It's a long break and long pre-season, we have time."