Barcelona have launched a campaign urging fans to “express their sympathy” in support of forward Lionel Messi after he appealed against a 21-month prison sentence for tax fraud imposed by a Catalan court.

Messi and his father, Jorge, were sentenced on Wednesday after a Barcelona court found them both guilty of three counts of defrauding the tax department to the tune of €4.1 million.

Messi’s management company said last week that the pair would take appeals to the supreme court, even though neither man is likely to serve any time in prison.

Under Spanish law, sentences under two years are usually suspended but, nonetheless, Barca have called on supporters to voice their “unconditional support on social networks”.

A Barcelona read: “FC Barcelona has set up a campaign in support of Leo Messi following the sentence issued last week against the Argentinian and his father.

“Using the hashtag #WeAreAll-LeoMessi while posting a photo or message with both hands open, the campaign is encouraging all Barca fans to express their sympathy for the greatest footballer in the world by voicing their unconditional support on social networks.

“By making it clear that #WeAreAllMessi, we want Leo to know that he is not alone. All members, supporters clubs, fans, athletes, media and everyone else are invited to participate.”

The long-running case relates to a scheme to avoid paying €4.1 million of tax on Lionel Messi’s image rights.

Meanwhile, Barcelona’s president Josep Maria Bartomeu took to social media himself to express his support.

He wrote on his official Twitter page: “Leo, those who attack you are attacking Barca and its history. We’ll defend you to the end. Together forever!”

The 29-year-old forward joined the club’s renowned academy in 2000, aged 13.

He made his competitive debut in 2004, at 17, and has now scored 453 goals in 531 appearances, winning five Ballon d’Or trophies for the world’s best player along the way.