Messi signed his latest contract in 2017, with the deal running until the end of the 2020-21 campaign.
Club president Bartomeu has now confirmed those reports, though he insisted Barcelona are not worried Messi will take up the option to leave, revealing Andres Iniesta, Xavi and Carles Puyol all had similar clauses.
"Messi has a contract that we signed two years ago and it runs for four years," Bartomeu told Barcelona's website.
"Before the last season, 2020-21, he can leave Barcelona, retire from football or play where he likes.
"Iniesta, Xavi and Puyol also had those clauses. For those players and Leo Messi, we don't need to worry.
"I doubt he'd want to play for another club, but he has earned liberty over his future. He's a big Barca fan and I have no doubt he'll want to continue until 2021 and we hope another year too."
Messi sustained an injury during pre-season and is yet to make an appearance this term, with Barcelona having gained just four points from their opening three LaLiga fixtures.