Okay, Neil's side can't finish any higher than fourth in the group, which is such a huge disappointment for everyone, given how well they did last season.
But, no one at the club will want to finish the campaign without rediscovering the kind of form they were showing before the two disappointing performances against Ajax in Amsterdam then when AC Milan came to Parkhead.
That's not what they want to carry with them all the way through to the start of next season's European campaign.
They will be determined to get back to the form they showed in the first three games of the group, especially the opening match in the San Siro which was the best they have played in any of the five ties.
Of course, they didn't take anything from that game in Milan, even though they deserved to. That was down to a failure to take the chances they created, a recurring problem for them in the Champions League this term.
In the last two games, those chances have dried up. But, it has been the overall level of performance which will have caused Neil most concern.
Having Scott Brown back will help because, when he is in the team, the level of performance is not allowed to drop to the low point it did when they lost to Ajax and Milan in Glasgow.
People will be watching closely to see how he reacts when he meets up again with Neymar. If it was me, I'd just ignore him and put the entire incident behind me.
Celtic appeared to have found the answer to their infamous poor away form, but Amsterdam showed it is not too far below the surface as they slipped back into bad habits.
If they can put in a good performance in the Nou Camp, it will provide proof this was just a blip - albeit a costly one.
Finishing bottom of the group is no disgrace as that is where Celtic's seeding says they should finish.
But, expectation was raised - perhaps unreasonably - after last season's exploits when they over-achieved.
Taking the last few years as a whole, no-one can be over-critical of Celtic.
It's just the last couple of games which have been the real disappointment, and tonight can restore belief for everyone.
That will be important as they don't want to have any question marks hanging over their heads when the qualifiers begin again next summer.
And, when the final whistle goes tonight, let's hope we are only talking about what the players did, not about fans' behaviour.
The eyes of Europe will be on the Celtic supporters after the behaviour of some recently.
After Friday's events, the club had no option but to act in the way they did.
Let's hope the strong message finally sinks in.