Messi, who scored more than 70 goals for Barca in all competitions last season, is currently committed to the club until the summer of 2016, but Rosell stressed the importance of getting work on an improved deal for the player under way as soon as possible.
"It finishes in 2016, but it would be irresponsible to not improve his contract," Rosell told Catalunya Radio.
"You have to think about such things. Right now there is nothing scheduled, but this is a machine that is constantly in motion and things can change at any moment.
"The coaching staff think about next Sunday - we look further down the line and take the more distant future into consideration. Work has to start now on the contract that will take effect from 2016."
The president also refused to be drawn on the current situation at Real Madrid, a matter which has occupied the Spanish press, who appear to be convinced that manager Jose Mourinho is fighting a dressing room revolt.
"The day you become preoccupied by other teams' matters is the day you start to lose," he said. "We need to remain a close group and work as such."