Iniesta had been Barca’s captain since 2015 when Xavi Hernandez left for Qatar, but he moved to Japanese side Vissel Kobe earlier this summer.
Messi, 31, has in the past led Barcelona in Iniesta’s absence but will now begin the campaign as the club’s outright captain.
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Sergio Busquets has also emerged Barcelona’s second captain, a role previously held by Messi.
The third and fourth captain spots, which have opened up owing to Iniesta and Javier Mascherano’s exits, will be filled by Gerard Pique and Sergi Roberto.
Sergi Roberto captained an inexperienced Barcelona side during the club’s recent tour of the United States.
All four of Barcelona captains were chosen through the club’s La Masia youth academy and only Pique – who had spells with United and on loan at Real Zaragoza – has played senior football away from Camp Nou.