In terms of qualification, this match means little. In terms of pride, it means everything.
Celtic and Barcelona couldn't be more paradoxical in their journey towards this game.
They are, however, already out of the Champions League and now play purely for pride after winning only once in the group so far.
But they have qualified for the last 16 already, making this match important to them only in that they will want to ensure they finish top of the group (a surprise defeat here coupled with a Milan win would see the Rossoneri finish first).
There's also the need to continue to arrest the mini-slump (by recent Barcelona standards) following their 4-1 defeat of Segunda Division B side Cartagena on Friday.
The Catalan side currently sit top of both La Liga and Group H—but both positions are somewhat precarious.
Domestically, the form of Atletico Madrid means there is no gap at the top—only a goal difference of two keeps Barca top, despite only one loss so far.
In Europe, a Milan win over Ajax would mean the Rossoneri can still pip them to the top qualifying spot in the group if Celtic grab a shock win.
A draw might be enough, but it would be inconceivable for Gerardo Martino to start anything other than a strong team—he will want the win.
As such, barring a monumental performance from the visitors or a colossal collapse by la Blaugrana, it should be a case of business as usual for the European giants.
Chilean forward Alexis Sanchez may feel more confident facing Fraser Forster this time round after scoring twice against him recently when the goalkeeper was on international duty with England.
Javier Mascherano, Gerard Pique and Neymar were rested during the Copa del Rey win over Cartagena, with at least two of them likely to feature on Wednesday.
In addition to Lionel Messi, who is still out with a hamstring injury, Barcelona are likely to be missing Cesc Fabregas to suspension as well as right-back Daniel Alves and goalkeeper Victor Valdes, both to calf problems.
However, both Xavi and Iniesta are included in the 20-man squad for the game, after recovering from a calf and hamstring injury, respectively.
Neil Lennon's side have played well against the Spanish champions three times in the past year—winning once and losing twice.
They've done it by defending bravely and hoping for clinical finishes when any chances arose; a system which worked to perfection just over a year ago with a 2-1 victory.
One of the defeats came with the final kick of the ball, snatching a famous draw away at the last possible second.
The other, at Celtic Park this time, came just two months ago and saw Lennon having to contend with Barcelona a player down after captain Scott Brown was sent off.
Since then the campaign hasn't really evolved for the Hoops.
The biggest decision the Celtic manager will have facing him this time round is what system to play.
It's Barcelona. At the Camp Nou. The natural inclination will always be to play for scraps, utilise Georgios Samaras as a target man wide left, to battle hard and hope to nick a goal, probably via a corner or free-kick.
However, the 4-4-2 diamond system Celtic have been playing recently has heralded some of the best passing football since Lennon's first full season in charge—he may opt not to change it.
The system seems to bring the best out of Kris Commons, who so often goes missing in European matches.
Charlie Mulgrew continues to impress as he gets used to playing in yet another new position as the midfield anchor, utilising his fantastic long-range passing to great effect in that position for both Celtic and Scotland.
It also necessitates Greek international Samaras dropping to the bench—unless he starts as a striker, which is generally when he is at his most frustrating and ineffective.
It will come down to Lennon's attitude to the game: Do Celtic play to their own strengths or to frustrate Barcelona's?
A big part of the recently successful system has been full-backs Mikael Lustig and Emilio Izaguirre marauding forward as the midfielders are playing more central—but Izaguirre is suspended. A semi-fit Adam Matthews may be thrown in at the deep end in a left-back berth he started in against the same opposition last year.
To choose the first option would be brave and, avoiding a heavy defeat, admired. But it's hard to hold it against anyone should they opt for the latter, given the opposition.
Gerardo Martino (via Barcelona official website):
We'll be playing in a 30 yard strip of pitch and we need to keep up the pressing to stop Celtic hitting us on the break. The most logical thing is that Neymar will start as the centre forward.
Neil Lennon (via the Daily Mail):
The shackles will be off a little bit but there has to be a defensive discipline and a concentration there. If we get carried away, we’ll be punished.