Even when you consider the well-reported exit clause in his contract, until recently the idea of Lionel Messi leaving Barcelona for another club was virtually unthinkable.
But this week friction has started to appear, with Messi publicly calling out Barca director of football Eric Abidal for bad-mouthing players in an interview, saying that "many players weren't satisfied nor working hard and there was also an internal communication problem" before Ernesto Valverde's sacking.
READ: Guardiola: Barcelona will need time when Messi leaves, like Madrid did post-Ronaldo
Messi's forthright response on Instagram said the "sports management must also assume their responsibilities" and suggested Abidal should name specific players if he is willing to criticise them, otherwise "we are all getting dirtied and feeding things that are said but aren't true".
Barca has since assured – via Spain's sports newspapers – that all is well, the pair have reconciled and Abidal will keep his job, but that is unlikely to dispel concern among supporters, particularly following further reports several other clubs have registered an interest.
Nevertheless, arguably for the first time ever, the prospect of Messi leaving does not seem an impossibility, particularly given a contract clause allows him to leave for free – but where would that leave Barca?
READ: Messi looks like he has 'one foot out of the door': Carrasco
A BRUTAL GENIUS
Declaring Messi important to Barcelona would be an understatement akin to saying the Titanic was big. After all, he's helped them win 34 trophies.
Messi made his breakthrough in the 2004-05 season and his impact has been almost beyond comprehension. If the six-time Ballon d'Or winner isn't the greatest footballer of all-time, good luck making a case for anyone else.
He has gone on to play a role in 864 goals (622 goals, 242 assists) in 711 matches across all competitions, a truly astounding feat.
One gets an even greater perspective of his influence when considering how much of Barca's overall total that equates to.
Across the same period, the Blaugrana have scored 2,241 times, meaning he has had a hand in 39 per cent of all of its goals over a period of almost 16 years – including his first season when he featured on just nine occasions.
Since the 2007-08 campaign, his first with more than 20 involvements, that figure shoots up to 44 per cent – or 804 of Barca's 1,812 goals in that time.
Given some of the players he has featured alongside, it is probably a step too far to suggest Barca has been a one-man team since Messi made a first-team role his own.
However, there can be little denying he has often carried them and no one else has had a remotely comparable impact.
Over the past 12 seasons, Messi has finished as Barca's leading scorer across all competitions in all but one - 2015-16 when Luis Suarez plundered 59.
His best was that remarkable 2011-12 campaign when he scored 73 goals across all fronts, while a haul of 29 assists took him to 102 involvements - 54 per cent of the team's total.
Where do you even start when planning to replace a player who has been directly involved in almost 50 per cent of your club's goals in a 12-and-a-half-year period?
One would hope for Barca's sake it has some form of contingency plan, but even if it does, it's difficult to imagine the club being able to buy anyone anywhere near as influential.
Messi is more than a mere footballer – Barca teams for more than a decade have been built with the purpose of getting the best out of him, while he is virtually unrivalled both as a creator and finisher.
Neymar is the obvious candidate to replace Messi when the time comes, as he does offer a similar blend of deadliness and craft, although Barca's financial constraints are well-documented and it's hard to see how the club could afford him at the moment, even without Messi's wage.
The club may opt to go down the route of signing a more singled-minded attacker, such as Kylian Mbappe or Lautaro Martinez, but again, certainly in the case of the former, affordability may be an issue.
Even if Antoine Griezmann manages to belatedly blossom in Barcelona colours, Messi's eventual departure will leave a gaping chasm that its current squad is unequipped to fill.
Putting together a post-Messi Barca could just be the single most fascinating rebuilding job in football history – but Josep Maria Bartomeu and Abidal will be clinging on to the hope that won't be for another few years yet.