Messi suffered the injury in last week's first leg in Paris, which ended 2-2, and had to be substituted at halftime.
The Argentine missed Saturday's 5-0 La Liga win against Real Mallorca at the Nou Camp, when his replacement in the roving forward role, Cesc Fabregas, netted a hat-trick.
"Messi did physiotherapy and recuperation followed by some fitness work on the pitch," Barca said in a statement on their website (www.fcbarcelona.es) without specifying whether he would be available to face PSG.
Forward Pedro and defender Adriano had a more intense workout and are likely to be fit.
"They do not yet have the medical all-clear but it's already the third day they are working with their team mates," Barca said.