Aguero is out of action with a knee injury after falling awkwardly in last week's Premier League opener against Southampton and the club are not expecting him back until mid-September at the earliest.
But that has not stopped Argentina coach Alejandro Sabella naming the 24-year-old in his squad for World Cup qualifiers against Paraguay and Peru on September 7 and 11 respectively.
Mancini accepts Argentina have a right under international rules to summon Aguero - and can carry out their own medical assessment if necessary - but he thinks it is a ludicrous situation.
The Italian said: "It is impossible because Sergio needs a minimum of two weeks without training. After two weeks he can start again.
"If in one week if he could be ready to play it is different, but I think he needs another two weeks.
"He can go and fly back quickly. These are the rules and we need to respect them - they are ridiculous rules."
City had initially feared a longer lay-off for their £38million club record signing, who scored 30 goals last season.
Now they hope he might be able to feature at Stoke on September 15 if his recovery goes well.
"We are lucky with Sergio because he can be very strong after injuries," said Mancini.
City travel to Liverpool on Sunday before preparing for what could be a busy week ahead of Friday's transfer deadline.
Mancini has said he expects some activity and will only sanction sales if he has replacements lined up.
With winger Adam Johnson having now left for Sunderland, additions are presumably in the offing but Mancini has given little away.
Italy midfielder Daniele de Rossi remains a strongly rumoured target despite the player's recent assertions that he wants to stay at Roma.
When asked if De Rossi was still of interest, Mancini said: "I don't know this. It is a difficult situation and I don't know what can happen."
On the general picture, he said: "I am sure we will do what we want in one week.
"We are working, We can't say a name or how many players, but in the last days we will be working."
Mancini said "his cost is too big" when asked about Athletic Bilbao enforcer Javi Martinez, who is thought to have a £31million release clause in his contract.
He added that "we don't have any chance" of signing Liverpool defender Daniel Agger.
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