Lionel Messi Photo: VCG

Lionel Messi has informed Barcelona he wants to "unilaterally" terminate his contract with the Spanish giants after a calamitous end to the season, a club source confirmed to AFP on Tuesday.

Lawyers for the Argentina star sent Barcelona a fax in which they announced Messi's desire to rescind his contract by triggering a release clause, sending shock waves throughout the world of football.

Barcelona have yet to officially react but are understood to believe the clause expired in June and that he remains under contract until the end of the 2021 season.

"In principal, this clause expired on June 10, but the unusual nature of this season disrupted by the coronavirus opened the way for Messi to ask to be released from his contract now," wrote Spanish sports daily Marca.

"It's the first step towards opening negotiations over his departure, on the basis of which his release clause amounts to 700 million euros [$828 million]."

Messi joined Barcelona's youth academy at the age of 13 and made his debut in 2004 as a 17-year-old.

The six-time Ballon d'Or winner is the club's record scorer with 634 goals and has won the Champions League four times. 

But his future at Barca was thrown into serious doubt following a humiliating 8-2 loss to Bayern Munich in the Champions League quarterfinals in Lisbon 11 days ago. 

It marked the first time Barcelona had conceded eight goals in a game since losing to Sevilla 8-0 in the 1946 Spanish Cup.

The humbling defeat sparked drastic changes within the club. Coach Quique Setien was sacked after barely six months in charge while sporting director Eric Abidal was also dismissed after Barca's first season without a trophy since 2007.

Argentine sports daily Ole described ­Messi's wish to leave as a "complete bombshell," but he has had regular disagreements with the club's board in recent times.

'More out than in' 

According to Spanish media, Messi met with new Barca coach Ronald Koeman last week and told the Dutchman he saw himself "more out than in" the club.

Koeman has vowed to "fight to put Barca back on top" and said at his unveiling he was hopeful Messi would remain at the club for several more years.

Since his appointment though, Koeman has reportedly told Luis Suarez he is no longer part of Barca's plans, delivering a similar message to Arturo Vidal, Ivan Rakitic and Samuel Umtiti.

"The club needs changes," said defender Gerard Pique following the Bayern demolition. "Nobody is untouchable, least of all me. Fresh blood is needed to change this. We've hit rock bottom."

The loss, Barca's heaviest in Europe, exposed an ageing team that Messi repeatedly had said was simply not good enough.

He said it in February and again in July, when a rant in the aftermath of handing Real Madrid the title turned into a brutal, but honest, assessment of their season. 

As his relationship with the club hierarchy grew increasingly strained, Messi also reacted publicly when Abidal appeared to blame the players for the sacking of Ernesto Valverde in January. 

He also led the fightback from the Barcelona players over a dispute with the board in March regarding pay cuts during the coronavirus pandemic.

"Respect and admiration, Leo. All my support, friend," tweeted Barca great Carles Puyol, a longtime former teammate of Messi, to which Suarez replied with two applause emojis.

Vidal also posted a cryptic message on Twitter. "When you shut a tiger in a cage he doesn't give in, he fights back," he wrote.

Messi's reported salary of nearly 1 million euros per week would limit the number of potential suitors able to afford his services while respecting UEFA's Financial Fair Play regulations. Manchester City, Paris Saint-Germain and Inter Milan are among those to have been linked with an audacious swoop for one of football's all-time greats.

"I don't see him anywhere else. I can't believe it. I prefer to think it's an ultimatum given to management for Bartomeu to go," said Ruben Tejero, a 28-year-old Barca fan among a group of around 100 supporters who gathered in front of the Camp Nou, calling for the resignation of under-fire president Josep Maria Bartomeu.