It is understood that Leo Messi would be able to start training with Barça's first team squad before he signs a new deal with the club. In other words, he would be allowed to train without officially being a Barcelona player. The Argentina captain is currently a free agent, and therefore unattached from any domestic club.
Two things need to happen for this to take place.
One. FC Barcelona would need to authorise the player to train with the squad.
Two. Leo Messi would need to take out medical insurance that would cover him for the duration of this unique situation. Something similar happened in this summer's Copa América, where Messi took out his own medical insurance in addition to the one that had been taken out by the Argentina Football Association. As soon as he signs a new contract at Camp Nou, he would then be covered by the club's medical insurance policy.
Barça won't need to register Messi with the RFEF when he extends his contract.
As revealed by SPORT, Leo Messi's licence as a Barça player for the upcoming campaign will not require a new registration. Even if the Argentina forward signs a new contract, following the expiration of his previous one, Barça will just need to pay the €1,200 requested by the RFEF for all new players: both those who were already part of the squad and those who arrive from other teams in LaLiga.
Barça already paid the first registration fee back in the day, so it will not need to pay the €54,692 registration fee set by LaLiga and the RFEF for signings from non-Spanish clubs. If Barça needs to pay this fee for its new summer signings - despite arriving on free transfers - Barça would need to pay nearly 200,000 euros.