Aguero has been sidelined since suffering a knee injury in City's season-opening Barclays Premier League game against Southampton four weeks ago. That did not stop Argentina coach Alejandro Sabella naming him in his squad for World Cup qualifiers against Paraguay and Peru.
Mancini accepts Argentina had a right to call up the player to conduct their own medical assessment, but does not think it helped his recovery. Mancini said: "He went there for five days, he worked with the physio. The Argentina manager wanted him there. This is a stupid rule because if we had a player who is injured for two weeks it is better he stays here."
Mancini described the rule as "ridiculous" when he first heard of Aguero's call-up and had hoped the player would be allowed to stay in England.
Despite that, Aguero was due to undergo a fitness test prior to Saturday's encounter with Stoke.
The club's £38million record signing resumed training earlier this week in the hope of possibly featuring at the Britannia Stadium.
Ideally, Mancini would like to give his top scorer from last season a run out ahead of next Tuesday's Champions League game at Real Madrid.
Mancini said: "Sergio is not 100% but his knee is okay. Maybe he could be on the bench."
Mancini must also decide when to hand new signings Maicon, Scott Sinclair, Javi Garcia and Matija Nastasic their debuts.
Despite completing the deals a fortnight ago, Mancini has had only limited time to work with the players due to the international break.
Source: PA
Source: PA