Messi back in training for Barcelona
"The big novelty of this Thursday's training session was Leo Messi," Barca said in a statement on their website.
The Argentine World Player of the Year damaged the muscle during Barca's quarter-final first leg at Paris Saint-Germain on April 2.
He sat out their 5-0 La Liga victory at home to Real Mallorca four days later but came on for the final half an hour at the Nou Camp last Wednesday to help a nervous Barca squeeze past PSG into the last four on away goals.
Midfielder Sergio Busquets, who has a minor groin problem, completed some work with the rest of his team-mates on Thursday after missing Wednesday's session, Barca said.
The La Liga leaders are chasing a third European crown in five years and play their semi-final second leg at home to German champions Bayern on May 1.