Having finally cleared one long standing Champions League hurdle with their away win in Moscow, Celtic must topple giants this evening.
Barcelona away is a fixture that makes most teams tremble. It looks a hopeless journey for our plucky Scottish champions, a side who have only just registered a maiden away win in this competition.
If Celtic will be prohibitive favourites in all their domestic matches this year they must accept the role of underdogs tonight.
As Gary Linton recalled in his post last night, it's not that long ago since Celtic were knocking Barcelona out of the UEFA Cup or taking a rare Champions League away point at the Nou Camp.
Not that long ago, but it feels like a footballing lifetime. In the intervening years Barcelona have come as close to any team of our generation to reinventing how football should be played.
Celtic, in common with most sides, have been stranded in their wake, stuck playing the football of mere mortals.
Abandon hope all ye who enter Catalonia?
But, as Jose Mourinho was rather narkily explaining recently, Barcelona are not currently Spanish or European champions.
There has also been a vulnerability at times, a reliance on a mismatched defence made up of converted midfielders.
Unfortunately for Celtic they retain the ability to simply score more than the opposition no matter how many they concede.
Every silver lining has a cloud.
All this could be good news for the myopic Celtic fan or the neutral with an inkling for a shock.
Because a winning bet on Celtic this evening would be a lucrative affair.
A Barcelona win is priced at 1/12. A Celtic win is a whopping 20/1. The draw is 10/1.
If a football match is a two horse race then the bookies see this one as a sprint between Frankel and Robert Louis Stevenson's Modestine.
Gary's prediction of a 2-1 Barcelona win is 12/1. By contrast a 1-0 win for Celtic is out at 40/1, remarkably the same price as a 7-0 win for Barcelona.
Celtic's ambitions in this competition are likely to be realised away from their two clashes with Barcelona.
Anything tonight would be a huge result and a massive bonus. It looks highly unlikely.
Celtic will need to thrive without much sight of the ball, they'll also need to figure out a way of stopping the superlative stealing Lionel Messi without giving Barcelona's other stars room to thrive. It could be like trying to herd cats.
Better sides than this Celtic team have failed to do any of that successfully.
I've got to - and I suspect I'll not be a lone voice here - plump for a comfortable Barcelona win.
3-0 at 11/2 or 4-1 at 12/1.
David deserves more glory in this competition. But tonight should belong to Goliath.
All odds from Ladbrokes #gameon
Always remembering www.gambleaware.co.uk