The Argentine and his father Jorge Messi are due to appear in court on Friday morning in the coastal town of Gava near Barcelona, where the player lives, accused of evading tax on Messi's image rights to the tune of 4.16 million euros (USD 5 million, 3.5 million pounds) between 2006 and 2009.
Despite the looming court case, Messi's form on the field has scarcely been affected with the Barcelona forward scoring 10 goals in just seven matches this season as the Spanish champions remain unbeaten.
"I am not worried, I'm always on the sidelines of all that, just like my dad. We have our lawyers and our advisors who handle these things. We trust in them and they will solve the issue," he said back in July.
The case began in June when a prosecutor accused the Messis of evading tax by ceding the image rights of the player to "purely instrumental entities" in tax havens like Belize and Uruguay.
According to the prosecutor's report, Messi "obtained significant income" from image rights between 2006 and 2009 on which he "should have paid tax in his subsequent declarations" to the authorities and never did.
A week later, a judge accepted the footballer and his father had a case to answer and ordered for them to appear before the court.
Although the offences of which both men are accused are in principle punishable by a jail sentence, the Messis paid the tax authorities five million euros in August (the 4.16 million euros claimed by the taxman plus interest), which will significantly reduce any sentence should they be found guilty.
The news caused astonishment in Spain where Messi is looked upon as a more humble figure than other football stars, particularly his Real Madrid rival Cristiano Ronaldo.
"Messi is a very good player and he doesn't have a conflicting image. Rather, he has a very professional image, of being focused on what he does and very close to the public," says Carles Canto, a marketing expert for IMG Consulting.
However, despite the initial consternation, the player's popularity doesn't appear to have diminished at all due to the allegations.
"Messi's image amongst Barcelona fans is so solid that it is very difficult for it to be clouded by this case," adds Enric Baneres, a sports journalist for Catalan daily La Vanguardia.
"Tax evasion is something so common in Spain like the siesta or paella that the people are very permissive with it. "A fan doesn't want to criticise their idols, so they are used to excusing them or putting the blame on someone else."
In this case the player's defence seems set to try to exonerate him of any responsibility and point the finger at his former agent Rodolfo Schinocca.
According to a document sent by Messi's father to the court, obtained by Catalan daily El Periodico, Schinocca was put in charge of organising the "structure and management" of the income from Messi's image rights.
However, Schinocca told Spanish radio station Cope that he had nothing to do with the case at hand because he stopped working with the Messis in 2006, before the supposed offences took place and accused Jorge Messi of wanting an off-shore account to manage the income from the image rights.
Whilst Messi's 323 goals in 387 games for Barca have made him irreplaceable on the field, his income from endorsements off it has also soared.
Between 2007 and 2009 he earned more than 10.17 million euros in image rights, whilst American magazine Forbes make him the 10th highest paid sportsman in the world with an annual income of USD 21 million from endorsements alone.
Despite the court case, Messi continues to lead advertising campaigns for brands like Adidas and video games maker EA Sports, whose latest version of the immensely popular FIFA franchise is released in Spain the day before Messi is due to appear in court with the Argentine on the front cover.
"Whilst the player is so good and his behaviour is quite normal and proper, it will not affect him too much," suggests Canto, adding that according to a study carried out by his firm in 2012, Messi has the best image of any foreign sportsman in Spain.