Messi, enjoying another stunning season in front of goal, played no part in Argentina's friendly wins against El Salvador and Ecuador during the international break.
The 27-year-old superstar's availability was placed in doubt when Argentina boss Gerardo Martino - formerly of Barcelona - and international team-mate Sergio Aguero stated he was complaining of discomfort when putting his football boots on.
However, Messi took part in light training on Thursday before joining the rest of Barca's squad for a full session on Friday - boosting the chances of La Liga's all-time scorer playing at the Estadio de Balaidos.
Barcelona's 2-1 El Clasico victory over Real Madrid last time out moved them four points clear of their rivals at the top of the division.
That crucial win has given them breathing space but they would be foolish to take Celta lightly.
Celta, who sit 10th, beat Atletico Madrid in February, a result that significantly dented the reigning champions' hopes of retaining their title.
And he will be more than aware of his former side's many threats on a weekend that will see Barca keen to avoid a slip-up, with Real expected to pick up all three points at home to second-bottom Granada.
Indeed, Celta claimed a stunning 1-0 win at Camp Nou earlier this season.
Joaquin Larrivey's goal settled November's clash, meaning that the Catalan giants will be out for revenge.
