Madrid

Six-time Ballon d'Or winner Lionel Messi told Barcelona he wants to leave -- on a free transfer -- in a "bombshell" fax on Tuesday that is expected to spark a legal battle over a buy-out clause worth hundreds of millions of dollars.

Signalling the end of an era at Barcelona, where Messi is the record scorer and has won four Champions League titles, the disgruntled Argentine wants to terminate his contract "unilaterally" by triggering a release clause, a source told AFP.

Relations have plummeted this year and speculation swirled about Messi's departure after this month's humiliating 8-2 Champions League quarter-final defeat to Bayern Munich, which left Barca without a trophy for the first time since 2007.

The 33-year-old's demand, faxed by his lawyers, prompted protests against Barcelona's under-fire president Josep Maria Bartomeu outside the Camp Nou where Messi, synonymous with the club's most successful period, is worshipped by fans.

"I don't see him anywhere else. I can't believe it," said Ruben Tejero, 28, one of about 100 fans at the stadium calling for Bartomeu to resign.

"I prefer to think it's an ultimatum given to management for Bartomeu to go."

Manchester City, Paris Saint-Germain and Inter Milan are among those to have been linked to Messi, who is among the greatest players in history and has wages to match, with a reported weekly salary of nearly a million euros.

ESPN reported that Messi spoke last week with Manchester City manager Pep Guardiola about a possible move. A Barcelona-based Brazilian journalist also said Messi wants to play under his former Barcelona coach.

Release clause

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

"In principle, 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, before going on to score a club-record 634 goals.

But his future at Barca was thrown into serious doubt by the 8-2 loss to Bayern, the first time Barca had conceded eight goals in a game since losing to Sevilla 8-0 in the 1946 Spanish Cup.

The defeat has sparked drastic changes. Coach Quique Setien was sacked after barely six months in charge, and sporting director Eric Abidal was also dismissed.

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

But 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.

Rock bottom

"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."

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.

The Lisbon 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 long-time former team-mate of Messi, to which Suarez replied with two applause emojis.

Vidal also tweeted: "When you shut a tiger in a cage he doesn't give in, he fights back."