When Aguero missed last weekend's draw at Stoke, City assistant manager David Platt claimed the star had suffered a minor ankle injury in training the day before.
But City boss Roberto Mancini turned what seemed a routine fitness issue into a more intriguing situation when he revealed his frustration at the "stupid" injury that has forced Aguero out of Saturday's clash against Sunderland.
"Sergio has a problem in his foot but it is better we don't talk about it because it is a stupid injury," Mancini said.
"It is not his fault but he can't play with this injury for a week, 10 days, two weeks?.
"It is a stupid injury. It didn't happen at home, it happened here (at the training ground)."
When pushed, Mancini insisted that Aguero had not dropped something on his foot, been tackled by a team-mate or kicked a door, adding: "I'll tell you when the season is finished".
Mancini's comments sparked a chase to discover the truth behind the injury that threatens to derail City's bid to overhaul leaders Manchester United at the top of the table.
The Daily Mirror reported Saturday that Aguero had damaged his foot while riding on a child's motorbike as he played with his young son at their Cheshire home.
The Mirror said Aguero had treated the injury using anaesthetic freeze spray, which had caused his skin to blister.
However, The Sun claimed Aguero's problem stemmed from an injury sustained against Chelsea earlier this month, which was then exacerbated when the club's medical staff applied a spray treatment that "resulted in an allergic reaction, causing the foot to balloon and blister as if it had been burnt".