The 32-year-old missed the whole of Barca's pre-season programme and was not part of their squad for the 1-0 loss to Athletic Bilbao on the opening day of the LaLiga season.
Messi – whose last competitive outing was for Argentina in the Copa America third-place play-off victory over Chile, a match in which he was controversially sent off – has been doing solo exercises to build up his fitness and sat out the LaLiga champions' first training session on Wednesday but was pictured with the rest of his team-mates later in the day.
Barca head coach Ernesto Valverde may now consider the Argentina international for selection against Real Betis on Sunday, with Ousmane Dembele and Luis Suarez already ruled out.
👏 Back in training with the group 😍 pic.twitter.com/D2Nk5FFNXm— FC Barcelona (@FCBarcelona) August 21, 2019
Dembele will miss the next five weeks with a hamstring injury and Suarez is out for an indefinite period after injuring his right calf in the shock defeat to Athletic.