But the supporters were not the only ones who appeared to be in some discomfort in the wake of Parkhead club's sojourn to Spain.
By the look of Neil Lennon's team on Saturday, many of the players had not quite got over their exertions in the Catalan capital either.
The champions were, despite being freshened up with several new faces, decidedly flat against Kilmarnock and suffered an agonising result as a consequence.
They could have no complaints, none whatsoever, about slumping to a shock 2-0 defeat to Kenny Shiels' side in the SPL showdown.
The visitors' keeper, Cammy Bell, had perhaps two saves of note – from a long-range Charlie Mulgrew free-kick and a Gary Hooper shot from an acute angle – to make in the entire 90 minutes.
Yes, the Rugby Park club got lucky at their opening goal just before half-time; Adam Matthews and Efe Ambrose both switched off to allow Cillian Sheridan the simplest of scores.
But there could be no denying the Scottish Communities Cup holders were the superior team on the day and were richly deserving of three points.
Celtic manager Lennon knows from personal experience just how much a big European game, particularly one away from home, takes out of an individual both mentally and physically.
The last time the Hoops competed in the Champions League in the 2007/08 season they played four away games against Shakhtar Donetsk, Benfica, AC Milan and Barcelona.
Gordon Strachan's side won just one of their subsequent domestic fixtures after returning to Scotland. Interestingly, they lost to Hibs away and drew with both St Mirren and Aberdeen at home following their outings in the continent's premier club tournament.
Heck, the great Martin O'Neill team Lennon himself was an important component of in the 2002/03 season lost a Scottish Cup game to Inverness Caley Thistle just days after beating Liverpool at Anfield in the Uefa Cup.
The Irishman understood that taking on opponents as renowned as Andres Iniesta, Lionel Messi and Xavi, to name just three, in the Nou Camp was always going to take its toll on his charges psychologically and drain their bodies.
Despite his disgust at the performance and his despair at a result that reduced Celtic's lead in the SPL to two points, then, he will not make any knee-jerk reaction to the loss.
Still, there will have to be a stark improvement by all concerned in the League Cup last eight tie with St Johnstone at Parkhead tomorrow or there may well be repercussions.
Lennon expected some of those who were brought into the team at the weekend – not least the Venezuelan striker Miku, fit-again midfielder Beram Kayal and fans' favourite Paddy McCourt – to stake claims for regular inclusion with strong showings.
But nobody in the Celtic team impressed greatly. It was only after Liam Kelly had buried the penalty that Kilmarnock were rightly awarded by referee Crawford Allan for Emilio Izaguirre's trip on Rory McKenzie in the second half that the home team started playing.
Celtic upped the tempo considerably and, with Hooper, McCourt and Tony Watt all being brought on in the second half, pushed hard to get back into a game that was slipping away from them.
But by then Kilmarnock could afford to sit back and protect their lead and they did so with the utmost professionalism.
Watt missed an open goal, but, in truth, even a draw would have flattered the hosts.
Lennon said: "I was confused. I couldn't understand how we produced a performance like that after I had refreshed the team. I thought we had a strong team out when the game kicked off.
"But there was no fluidity to our play, we were too passive, there was no intensity to anything we did. We got what we deserved without Kilmarnock having to do that much.
"Those that came in have to do better. There was a malaise to the team that I did not like at all. It is unacceptable, a dose of reality, back down to earth with a bump.
"It is the poorest we have played in my time in charge. I will be looking for a reaction tomorrow night."
Celtic fans demand their team wins every domestic match, no matter what the circumstances, where the game is or who the opposition are.
With the size and quality of their squad in comparison to those of their smaller and less wealthy top flight rivals it is a not unreasonable expectation.
So while the reverse to Kilmarnock, just five days after a meeting with arguably the greatest team of all-time, is perhaps understandable it is still far from being acceptable.
Normal service will have to be resumed tomorrow evening against St Johnstone or there will be repercussions for some of those responsible.
