The €700million ($833m) release clause in Lionel Messi's Barcelona contract remains valid and must be paid for his deal to be terminated unilaterally, LaLiga has said.

Messi has informed Barca he wants to leave the club and he is thought to have not attended pre-season medical tests with the rest of the first team on Sunday.

According to reports, the Argentina star believes the clause in his contract that allows him to terminate it at the end of each season - and thereby become a free agent - still applies because 2019-20 was extended to August due to the coronavirus pandemic.

However, Barcelona appear adamant this clause has long since expired and that the player's €700m buyout option must be paid if he is to be released.

In a statement issued on Sunday, LaLiga insisted Messi's contract can only be terminated by the player if the release clause is paid in full.

The LaLiga statement said: "The contract is currently in force and contains a 'termination clause' applicable in the event that Lionel Andres Messi decides to urge the early unilateral termination of the contract, carried out in accordance with article 16 of royal decree 1006/1985, of June 26, by which the special employment relationship of professional athletes is regulated.

"In compliance with the applicable regulations, and following corresponding procedure in these cases, LaLiga will not carry out the process for a player to be de-registered from the federation unless they have previously paid the amount of said clause."

Messi is reportedly determined to leave Barca, the club he joined as a 13-year-old, but any move would be complicated by the need for a suitor to pay a transfer fee.

Manchester City, Inter, Paris Saint-Germain and Juventus are said to be the most likely to sign him, but his substantial wages present a major obstacle in negotiations even before a transfer fee is considered.

Although Barca would be unlikely to hold out for €700m, they are likely to demand at least a nine-figure fee, even though Messi's contract expires in under a year.