The club confirmed on Tuesday that the Argentine sent a document expressing his desire to to activate a release clause that would end his contract and allow him to leave for free this summer.
Barcelona have received this in writing via a fax from his lawyers. They have not officially replied yet but are understood to be preparing one.
Barcelona do not agree the clause is still active. It is said to have expired on June 10 – 10 days after the original date of the Champions League final on May 30.
But Messi’s lawyers are arguing that – in the spirit of the deal and good faith – the clause is still active after the rescheduled final on August 23, which was delayed due to the coronavirus pandemic.
The announcement comes 11 days after Barcelona’s humiliating 8-2 loss to Bayern Munich in the Champions League quarter-finals, one of the worst defeats in the player’s career and in the club’s history.
Messi has won a record six Ballon d’Or awards during his time at Barcelona as the top player in the world, and has helped the club win 10 Spanish league titles and four Champions Leagues.
Koeman said: “I don’t know if I have to convince Messi (to stay). Of course he is the best player in the world and you want the best player in the world in your team – you don’t want him playing against you.
“For me as a coach, I would love to work with Messi because he wins matches. If he is at the ability and the level he has always shown, I would be more than happy for him to stay.
“He’s still got a contract and he is still a Barcelona player. There are some older players in the team and we need to make some decisions but in Messi’s case, I hope that he stays with us.”