Lionel Messi sat out Barcelona's opening preseason training session Monday, sources told Agence France-Presse correspondent Tom Allnutt, further escalating tensions between the player and club.

Messi's legal team argues he's unilaterally terminated his contract with Barcelona and doesn't need to show up to training, ESPN's Sam Marsden reports.

The 33-year-old already instructed the club's higher-ups Sunday that he wouldn't undergo the necessary coronavirus testing to participate in training.

Ivan Rakitic, who's reportedly set to return to Sevilla, also missed Monday's session, according to Allnutt.

A court case is now looming over Messi and Barcelona, as the two sides insist on different interpretations of a now-infamous clause in the Argentine's contract that may or may not allow him to leave on a free transfer.

The club reportedly maintains the clause in question expired in June and that any team interested in signing Messi must activate his €700-million release clause.

La Liga backed up Barcelona's version of events, saying in a statement Sunday that it will not sanction a transfer if the buyout fee isn't paid in full.

Barcelona reportedly believe Messi can only leave on a free transfer if he agrees to sit out the entire 2020-21 season.

Manchester City are apparently confident they have the inside track on signing Messi and are prepared to spend up to €150 million.