FC Barcelona have begun their training under new coach Ronald Koeman but as expected, star striker Lionel Messi was missing.

The Argentinian did not return along with the rest of his teammates for the start of pre-season training on Monday, after he refused to take a PCR test for COVID-19 on Sunday, reports Xinhua news agency.

Messi's decision is another step in his plan to leave the club where he has spent the last 20 years, with the striker and his advisors taking the stance that his contract with Barcelona allows him to leave the Camp Nou on a free transfer this summer.

This opinion is not shared by Barcelona or the Spanish Football League (LaLiga).

In a statement on Sunday, LaLiga supported Barcelona, saying that anyone who wants to buy Messi will have to pay his 700-million-euro release clause.

LaLiga is not a disinterested party in this affair, given that the Argentinian is its biggest star and the league has already lost Neymar and Cristiano Ronaldo in recent years.

The possible departure of the biggest name will see LaLiga lose ground to the Premier League (especially if Messi moves to Manchester City) and make it harder to demand high fees for TV rights.

Koeman held his first training session with just 13 first-team professionals and six players from the Barcelona B-team, with others such as Sergio Busquets and Ansu Fati reporting for international duty in Madrid.

Ivan Rakitic was another absentee as the 32-year-old Croatian is in Sevilla for a medical ahead of a return to the club that he left to join Barca in 2014.

Rakitic, who was recently told by Koeman that he was not part of his plans for the coming season, is expected to sign a three-year contract with the newly-crowned Europa League champions.