Messi, 33, is out of contract in June and, after trying to leave Camp Nou last summer, one of the first tasks facing the incoming president is to convince him to sign a new deal.
Joan Laporta, Victor Font and Toni Freixa are the three candidates. Messi has not publicly supported any of them, but Laporta has repeatedly claimed that he is the best-placed to keep the six-time World Player of the Year.
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Laporta was previously Barca president between 2003 and 2010, coinciding with Messi's progression into the first team and the six-trophy year under Pep Guardiola in 2009.
Font and Freixa have both expressed their confidence in keeping Messi if they are elected, too.
A successor for Josep Maria Bartomeu, who resigned in October, will be announced officially at 11.30 p.m. CET, with more than 100,000 club members eligible to vote. Voting is usually is restricted to Camp Nou but, due to the coronavirus restrictions, six polling stations have been set up across Catalonia and Andorra, with postal voting also included for the first time.
In addition to opening talks with Messi over a new deal, with Paris Saint-Germain and Manchester City among the clubs keen to sign him, the new president will also have to deal with the club's financial problems, with gross debt rising to €1.2 billion over the last year.
A decision on the Espai Barca project, which includes the renovation of Camp Nou, also needs to be made, with work frozen on the €825 million project.
On the pitch, an overhaul of an ageing squad started last summer but there are still big decisions to be made as Barca look to bounce back from a first trophy-less season since 2007-08.