Lionel Messi boycotted Barcelona’s first pre-season training session on Monday, club sources have confirmed to AFP, as the striker upped the stakes in his battle to leave this summer.

After skipping coronavirus tests on Sunday, Messi was absent again from the Ciutat Esportiva, where Ronald Koeman held a session at 5.30pm, his first since being appointed Barca coach.

It appears increasingly likely Messi will try to force a transfer by refusing to play in La Liga next season, which begins on September 12.

The Argentine’s lawyers believed that a clause in his contract with Barcelona would allow him to leave for free during the mid-season break but Barcelona have been adamant that the clause expired in June and any club wanting to sign Messi will have to cough up $833 million to activate his release clause and sign him.

Even La Liga backed Barcelona over the release clause on Sunday after releasing a statement.

“The contract is currently in force and has a ‘termination clause’ applicable if Lionel Andres Messi decides to activate the early unilateral termination of the contract,” La Liga said in a statement.

“In compliance with the regulations and procedure in these cases, La Liga will not de-register the player from the (Spanish football) federation unless they have previously paid the amount of said clause,” the Spanish league said in a statement.

But Messi has remained steadfast. His snub on Monday comes after he asked for a meeting, not to negotiate, but to begin facilitating an amicable and dignified departure.

Manchester City remain favourites to sign the 33-year-old, whose basic salary alone amounts to around 60 million euros.

If Barcelona and Messi decide to avoid a lengthy legal process, a compromise selling price of around 100 million euros could be within reach for City, while eliminating their less wealthy rivals.

Messi has reportedly spoken to City coach Pep Guardiola already but others remain in the running, including Paris Saint-Germain, Inter Milan and Juventus.