The Spanish champions' official Twitter feed reported that the four-time reigning world player of the year, who missed the end of the Primera Division season with a hamstring injury, had "received the medical discharge".
Argentina coach Alejandro Sabella had been positive earlier this week about Messi's prospects, but also insisted he would err on the side of caution if there were any doubts about the 25-year-old's fitness.
"I think his leg is well. He looks fast to me, but we have to analyse his inactivity. We do not need to take unnecessary risks," he said.
Sabella's side will tonight be looking to take another significant step towards sealing a place in next year's finals in neighbouring Brazil.
The Albiceleste can afford to not rush Messi back as they are in a strong position at the top of the South American qualifying group, lying four points clear of nearest challengers Ecuador.
However, they have also played a game more than the two teams immediately below them and a defeat at the Monumental stadium tonight would see third-placed Colombia close to within two points.