They have nothing else to play for.
Rafa Benitez will know what awaits him in the Nou Camp on Wednesday. Barcelona play fast, flowing attacking football and yet when they faced Chelsea in the group stages, they appeared very vulnerable to the counter attack. They are formidable but what they are definitely not is unbeatable.
Liverpool have cause for optimism. They can look back two years at the incredible atmosphere Anfield generated in European nights against Juventus and Chelsea and imagine they can repeat them.
If they have to go to the Nou Camp, shut the game out and return home with a goalless draw, then so be it. Benitez would take it now. In between, they have Manchester United coming to Anfield; this is two weeks that will shape Liverpool's season and Benitez knows it cannot be allowed to end on March 6.
It is a time for strong minds and what has happened at Liverpool's training camp in Portugal can hardly have helped. Whatever the truth behind the fracas involving Craig Bellamy and John Arne Riise, it will count for nothing once the players cross the white line to play but it will affect the build-up. Barcelona may have their own problems between Samuel Eto'o, Ronaldinho and the manager, Frank Rijkaard, but that is even more reason why Liverpool should have gone to Spain 100 per cent together.
A strong manager would ignore the personal animosities and play his best team. Bob Paisley would certainly have done so, whatever happened before the game. It is a big decision for Benitez, but Wednesday's match is full of massive decisions.
Who does he play at centre-back alongside Jamie Carragher? Does he go for the understanding Sami Hyypia has built up with Carragher over the years and his experience of the big occasion or look at Sami's lack of pace and wonder if his back line will be ripped apart by Barcelona's quick feet.
Chelsea and Manchester United have the opposite problem to Liverpool. They also need strong minds not because the Champions League is the only thing left to play for but because the big games are coming thick and fast. Their matches against Porto and Lille may be straightforward but they have to look to what lies beyond.
Both Sir Alex Ferguson and Jose Mourinho have won the Premiership and the Champions League before and they know the requirements of course and distance. If you study Cristiano Ronaldo; he is the best player in the country but he has never won the Premiership or the European Cup. There is a danger he might be led by events or miss the vital signs but in Gary Neville, Ryan Giggs and Paul Scholes he is surrounded by people who have been there.
They know that however tough the season appears in September and October, the real pressure comes in February, March and April, when a game against Watford can suddenly appear the most important of your life. They know that a dressing room can be the centre for the kind of euphoria that will take you on to the next game or a chasm where your hopes will be buried.
I have been in dressing rooms chasing three or four trophies in seasons where there were no cameras and you were only on the back or inside-back page of a newspaper rather than the front. You take the pressure with you on to the training ground and it is still there when you get home and it only ends when your season ends.