Manchester City manager
Mancini has been reluctant to discuss the problem, only referring to it on Friday as 'stupid', but did appear to confirm reports that the player's skin reacted badly to a spray used to treat a knock suffered in the recent win over Chelsea.
When asked if the spray was involved, Mancini, speaking after the Sunderland match, said: "Yes."
Mancini had spent the preceding moments trying to downplay the situation and again insisted no blame was attached to the 24-goal striker over the matter.
He said: "It was not his fault, like someone wrote in the newspaper this morning."
Mancini claimed some theories published as to how the initial injury might have been caused are 'not true'.
What he could not deny, however, was that the 23-year-old was badly missed as City missed the chance to move back to the top of the table.
Rival Manchester United could now pull five points clear with victory over Blackburn Rovers on Monday evening (Tuesday morning AEST).
Mancini said: "We missed Aguero and for this reason I am disappointed. I hope he can recover for the next game."
French defender Gael Clichy has signed a new four-year deal at Manchester City.