Jurgen Klopp’s side have squandered a comfortable position in Group C after losing two of their last three matches.
Their 2-0 loss at Red Star on Tuesday was a major blow given they had already lost to Napoli earlier in the campaign.
The Reds face Paris Saint-Germain in the French capital and Napoli at home in their final group game, with their progress to the last 16 suddenly uncertain.
A loss to French champions PSG would leave them facing a nail-biting shoot-out with Napoli and Liverpool midfielder Lallana knows his team have no excuses for their predicament.
Lallana, still edging his way back to full match sharpness after a period out with injury, knows it is time to step up for the team that finished as Champions League runners-up last season.
“As players we’ve got to take full responsibility and make sure it doesn’t happen again,” Lallana told LFCTV.
“It’s still in our hands — if we win our next two games we go through, but that was a great opportunity missed for us.
“It’s going to be very tough. That’s the Champions League — there are no teams that enter this competition that give you wins.
“It wasn’t like us and we need to move on and improve if we’re going to go through to the knockouts.
“Of course there’ll be a reaction. It’s not the first time we’ve lost games, it’s about how you react and bounce back, but we’re thoroughly disappointed to come away (from Belgrade) with nothing.”
Liverpool have won just three of their last nine matches, against Red Star, Cardiff and Huddersfield.
They conceded a goal from a corner and another from a loss of possession and quick counter-attack against Red Star.
“It was a slow start all round really and we gave them far too many opportunities, especially from set-pieces,” Lallana said.
“We had chances but we weren’t ruthless enough, weren’t patient enough. It’s not like us.
“It’s on us to take responsibility and we need to bounce back in the next two games.”
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