Pellegrini is convinced Aguero is still improving.
He said: "He arrived in Spain when he was 18 or 19 years old.
"He was always a very important player, a top player, but this year he is trying to work a little bit more without the ball.
"You see, three or four of the last goals we scored are because he is doing a good job pressing on their defenders. I think he is more complete.
"I said last week after Messi and he is the best."
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