The Argentine forward is widely expected to join French side Paris Saint-Germain (PSG) in the coming days after FC Barcelona said they could not afford to retain him.
That means the 34-year-old Messi is likely to share his perspective of the departure that has stunned world football.
His contract expired at the end of June and both parties had agreed fresh terms, only for FC Barcelona to announce the bombshell news on Thursday.
The Spanish club said they could not proceed due to “financial and structural obstacles”.
The club’s all-time record scorer, who has made more appearances for FC Barcelona than any other player, recently won the Copa America with Argentina.
He landed the Copa del Rey with FC Barcelona last season, adding to an array of trophies.
During his time at FC Barcelona, the only club of his professional career, Messi has helped the team win 10 LaLiga titles and four UEFA Champions Leagues.
Also, he has been awarded the Ballon d’Or a record six times.
FC Barcelona said Messi would address the media in the Auditori 1899, a large function room at the stadium, at 12:00 local time (1000 GMT) on Sunday.
The club added: “On Thursday, it was announced that the Argentine star would not be staying at FC Barcelona, where he has set club records for appearances, goals and official titles.”
There has been no indication of a change in FC Barcelona’s stance, with seemingly little prospect of a U-turn.
FC Barcelona’s announcement of Messi’s departure stated it was a move that “both parties deeply regret”.
The club cited “Spanish LaLiga regulations on player registration” as preventing them from handing him a new contract.
Like many clubs, FC Barcelona have been hit hard financially by the COVID-19 pandemic.
Heavy spending on players in recent seasons has largely not paid off, with Real Madrid and Atletico Madrid winning the most recent two LaLiga titles.
What Messi has to say about the recent chain of events is keenly awaited.
FC Barcelona president Joan Laporta said on Friday: “There was a moment when La Liga insinuated to us that the proposed contract could suffice.
”But, after a technical analysis by its financial commission, they then informed us that wouldn’t fully suffice either.”