Messi's shock departure earlier in the summer opened up the number 10 shirt.
Aguero, who joined the Spanish giants on a free transfer, was reportedly offered the legendary shirt number following Messi's transfer to Paris Saint-Germain.
But the former Manchester City star rejected the jersey due to his loyalties with Messi.
"Refusing to wear the number 10 shirt at Barcelona?" He said. "It wasn't that I didn't want to, but it was out of respect for Messi."
Philippe Coutinho was also briefly linked with the number 10 shirt, with attacking phenom Ansu Fati eventually receiving the famous kit.
The 18-year-old will the number 10 shirt as he follows in the footsteps of the aforementioned Messi as well as Rivaldo and Ronaldinho, among others.
As for Aguero, he will don the number 19 shirt.
The 33-year-old has yet to make his Barca debut following a calf injury sustained in training.
He could be available for selection next month, with fixtures against Atletico Madrid, Valencia and Real Madrid slated.
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