Lionel Messi was subjected to individual exercises once more on Tuesday as he continues his recovery from the back injury that ruled him out of Argentina's 2-1 Copa America win over Chile.

The Barcelona star sustained the problem during his country's friendly against Honduras on May 28 and has since been working towards a comeback.

He was forced to sit out Monday's Group D opener, but national team coach Gerardo Martino was optimistic after the match that Messi will be fit in time for their second game against Panama on Friday.

The 28-year-old still has work to do, though, as he was unable to participate in squad training on Tuesday.

Meanwhile, Lucas Biglia was also forced to sit out Tuesday's training as he joined Messi for an individual session.

The Lazio midfielder is recovering from a hamstring injury and also missed the win over Chile.