The Barcelona president is convinced that the Argentine superstar will clear his name following accusations of tax evasion towards the forward and his father, Jorge
The Argentina international, as well as his father, Jorge, stands accused of defrauding the state of some €4 million (£3.4m) between 2007 and 2009.
The 25-year-old soon voiced his surprise at the allegations and the club have voiced their confidence that their 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 (£511,000) faces a stretch of between two and six years in jail and a hefty fine.