Striker Aguero and defender Garay were both unused substitutes as Argentina's pre-FIFA World Cup preparations continued on Wednesday with a 3-0 win over Trinidad and Tobago on Wednesday.
And the Argentinian Football Association (AFA) have now confirmed that the pair face fitness battles as the start of the tournament looms large on the horizon.
Manchester City star Aguero has endured an injury-hit 2013-14 at club level and started just 20 of his side's 38 Premier League games en route to being crowned champions of England.
When fit, though, Aguero's influence was obvious as he scored 17 league goals and netted 28 times in total in competitions.
Like Aguero, Garay also heads to Brazil off the back of winning a domestic title as he helped Benfica top the Primeira Liga.
Question marks now remain over of what part - if any - Aguero and Garay will play in Saturday's final friendly with Slovenia.
Argentina's World Cup campaign begins against Bosnia-Herzegovina on June 15.
