Aguero told broadcaster TyC Sport: "The money isn't a problem here, but I think Messi, like Ronaldo, is a player who is a symbol of their club and it's hard for them to leave".
"Then one thinks 'why did I?', but it's hard to imagine that something like that could happen".
"I would love to have Leo on my team, but that seems quite complicated".
Messi proved his enduring class once again on Tuesday evening, scoring a hat-trick in Argentina's 3-1 win over Ecuador to nearly single-handedly send his side through to the World Cup finals.
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The City striker missed the game as he continues his recovery from a fractured rib suffered in a auto crash in Amsterdam. "I was very nervous but I screamed for joy. I thanked him for what he is doing for the World Cup".
Aguero, who suffered a broken rib in the collision, did not confirm whether he is in contention to feature in this weekend's Premier League clash with Stoke City.
He said: "When I got to the hospital I asked the doctor if I could play for City on the Saturday [against Stoke]". "I trained normally, but without the group". Back to training. I am ready!
City star Sergio Aguero says he'd love to see his Argentina team-mate at the Etihad stadium. "I know nothing. I saw the news and read that and I was surprised".