Lionel Messi's future at Barcelona remained unclear as his father published a letter to La Liga on Friday dismissing their claim that a 700 million euro ($830 million) release clause in his son's contract still applies if he wants to leave the club.

Six-times world player of the year Messi insists he can leave on a free transfer while Barcelona, backed by La Liga, argue that the release clause must be paid.

La Liga responded to Jorge Messi's letter with a statement reaffirming its support for Barcelona's stance that Messi's contract was still valid.

The 33-year-old Messi dropped a bombshell last month that he wanted to leave the club and that he could do so on a free transfer.

A further twist in the story that has gripped the sporting world came as Argentina's TYC Sports reported on their website that Messi had reluctantly agreed to stay with the Spanish club for another year.

Jorge Messi's letter was written directly to La Liga president Javier Tebas and accuses La Liga of making an error in their interpretation of the contract.

"First, we do not know what contract you have analysed and on what grounds you conclude that there is a 'release clause' applicable in the case of him deciding to unilaterally end his contract from the end of the 2019-20 season," he wrote in a letter published on social media.

"Second, that doing so (reaching that conclusion) is founded upon a clear error on your part. As clause 8.2.3.6 of the contract signed between the club and the player explicitly says: “This indemnity will not apply when the player’s decision to unilaterally rescind the contract is effective from the end of the 2019-2020 season," he added.

"It is obvious that the compensation of 700 million euros, provided for in the previous clause... does not apply at all."

La Liga originally issued a statement on Sunday, hours after Messi failed to attend a pre-season medical, saying that they would not approve a request for Messi to be de-registered as a player with the Spanish football federation, unless the amount in the release clause was met.

They underlined that stance in a further statement on Friday, despite Jorge Messi's insistence that his son's contract was no longer valid.

It means the frenzy of speculation about where Messi will play next season will continue unabated.

Should he leave Barcelona, Premier League club Manchester City are favourites to sign him, which would allow Messi to link up with his former Barca coach Pep Guardiola.

Although even the Abu Dhabi-owned club might find a 700 million-euro fee, plus Messi's huge salary, a deal-breaker.

Messi, who has won more than 30 major trophies with the Spanish club and scored more than 600 goals, earns around one million euros per week.

Messi informed Barca last week he wished to leave immediately, plunging the club into new turmoil less than two weeks after their humiliating 8-2 Champions League quarter-final defeat by Bayern Munich.

Messi's lawyers intend to invoke a clause in his four-year contract, signed in 2017, which would have allowed the forward to leave the club for free if he had requested it by June 10.

They will argue that that date nominally the end of the season is now irrelevant after the coronavirus pandemic forced an extension of the La Liga campaign deep into August.