BARCELONA (AFP) -- Lionel Messi missed a coronavirus test at Barcelona's training ground on Sunday morning, club sources have confirmed to AFP, raising the possibility he will now boycott preseason to force a transfer.

Without passing a coronavirus test, Messi will be unable to join teammates for new coach Ronald Koeman's first training session on Monday, with the start of the La Liga season less than two weeks away.

Messi was due to report for testing at 10:15 a.m. on Sunday but according to sources at Barca, he failed to show up at the Ciutat Esportiva.

The club's captain and greatest ever player could now be punished with a fine and even a reduction in salary if the strike continues.

Luis Suarez -- his best friend and strike partner -- and Arturo Vidal were among players seen arriving for tests, despite both being told they should find new teams as part of a planned clear-out this summer.

The meet-up was a chance for Messi to make his first public appearance since the burofax stating his intention to leave arrived in the offices of Camp Nou on Tuesday.

Instead, his absence offers a clear indication of his determination to secure a move and how ugly this dispute could now become.

Taking part in the team's preseason program could damage his legal case if his departure ends up being settled in court.

Barcelona insist a clause included in Messi's contract that allowed him to go for free this summer had to be activated by June 10 and is therefore no longer valid.

The only way the 33-year-old will be allowed to depart, the club argue, is through his release clause, set at 700 million euros ($833 million) until his contract expires on June 30, 2021.

But Messi's side believe the clause refers not to a specific date but to 10 days after the end of the season, which this year was extended into August due to the pandemic, with the Champions League final only played last weekend. (AFP)