Dejan Lovren has admitted Liverpool players felt "ashamed" after Saturday's shock 3-0 defeat by Watford.
Jurgen Klopp's side came unstuck in spectacular fashion at Vicarage Road, suffering their first loss of the Premier League season.
The reverse in Hertfordshire also ended Liverpool's 44-match unbeaten run in the top flight, having not lost since a 2-1 defeat by Manchester City in January 2019 before this weekend.
The Reds remain 22 points clear of the chasing pack as the club chases its first title in 30 years.
But Lovren, who deputised for Joe Gomez in Saturday's setback, thinks Liverpool will have to improve quickly if they are to win more than one trophy this term.
"It is strange, to be honest. It hurts, really hurts," he said after the match. "A defeat is a defeat but, you know, this was strange. Maybe it is a wake-up call for us.
"It feels like someone has hit us in the face - and we deserved it. We feel a bit ashamed because there's no excuse for that performance.
"It really hurts because from the beginning to the end we were missing all the things we usually have.
"The manager looked at us when he came into the dressing room and I think he knows we are missing something.
"I think it was about the aggression when we lost the ball and not recovering it as quickly as possible.
"Usually we do it without a problem but against Watford, they were always winning the second balls - and that doesn't usually happen with us.
"We need to look at this and realise that we have to do much, much better."
Liverpool will hope to return to winning ways when they face Chelsea in the fifth round of the FA Cup on Tuesday.
The Merseysiders then return to Premier League action against Bournemouth on Saturday.
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