Messi had been examined by Argentina team doctor Daniel Martinez and Barca medical staff and "both parties agreed that there have been considerable improvements", the La Liga club said on their website.
"The player will continue doing specific recovery exercises until he is ready to resume normal training with the rest of his team mates," they added, without specifying when that might be.
After leading Argentina to the World Cup final, where they lost 1-0 to Germany, Messi has made a bright start to Barca's La Liga campaign and scored twice in their 3-0 opening-day win at home to Elche last month.
He set up Barca's goal in their 1-0 success at Villarreal in their second outing but was diagnosed with the injury after the game. Argentina won Wednesday's friendly in Duesseldorf 4-2.
(Writing by Iain Rogers, editing by Toby Davis)