The Barcelona president is convinced the Argentine will clear his name following accusations of tax evasion towards the forward and his father
The Argentina international, as well as his father Jorge, stand accused of defrauding the state of some 4 million euros between 2007 and 2009.
The 25-year-old soon voiced his surprise at the allegations and the club has expressed confidence that its star is completely innocent.
"I've spoken to [Messi]'s family and they're very calm," Rosell said at a press conference.
"They have our full support because we believe Messi is innocent in this whole case."
Spanish law dictates that anyone found guilty of tax fraud exceeding 600,000 euros faces a stretch of between two and six years in jail and a hefty fine.