The attacker was forced to withdraw from the Argentina squad for Wednesday's friendly against Germany, which ended in a 4-2 win for the South Americans over their World Cup final conquerors.
Messi picked up the injury during last weekend's 1-0 La Liga win at Villarreal, and Barcelona issued an update on his condition on Thursday.
"The Argentina national team doctor, Daniel Martinez, and others from the FCB Medical Services have evaluated the groin strain sustained by Leo Messi during last weekend's league fixture away to Villarreal," read a statement.
"Both parties agreed that there have been considerable improvements, and the player will continue doing specific recovery exercises until he is ready to resume normal training with the rest of his team-mates."
Barcelona will be keen to have Messi back in contention for the start of their Champions League campaign, which kicks off at home to APOEL on September 17.