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In extracts revealed by M.E.N. Sport, Aguero tells of his fondness for his fellow front man and attempts to shed some light on what it was like sharing a dressing room with him.
'Mario was crazy when he wanted to be. He’d do daft things whenever he felt like it because he thought he could,' explains Sergio. 'We’d go out on the training pitch and he’d kick the balls away in different directions just to be silly, or he’d throw cheese over people when he was sat in the dining room.
A lot of his behaviour, I feel, came from a feeling he had that he was somehow different and maybe a little insecure. I couldn’t help but wind him up from time to time, calling him silly names and toying with him but he knew it was always in an affectionate way because I loved Mario – everyone loved him, though he drove us nuts at times.
'He used to say that nobody loved him and I’m sure he believed that was true, though it was anything but.'
In same book, Barcelona superstar Lionel Messi provides the forward, and reveals the first time he caught a glimpse of his international teammate on the pitch.
'I was in Rosario when I saw him on that first occasion, enjoying some time back in my home city,' he writes. 'I took the opportunity to watch the match that was being shown on television: Independiente vs. San Lorenzo.
'I remember little or nothing of the match itself. But I do recall the moment that they showed a boy in the Independiente squad who, I thought, must be about the same age as me, and who was about to make his debut.
'A year-and-a-half later, by which time I had already started to play in the Barcelona first team, I saw him again. It was a chance encounter at the Argentinian Football Association’s training complex at Ezeiza.
'A few months later, in June 2005, we were to come across each other again, this time as part of the Argentinian Under-20 squad that was going to compete in the World Cup for that age group over in Holland.We clicked right away. We were the youngest players in the squad, which meant that we spent more time together.
'What can I say about Sergio back then...? That he was a real character, a really sound guy, capable of listening and then saying exactly the right thing to let you know he was there for you or, with perfect delivery, to make you burst out laughing.
'And on the field, he was talented, a winner, a born competitor who never knew when he was beaten.'
The 26-year-old hitman is averaging a goal every 59 minutes in the Premier League this season, and has netted 11 times in 11 games across all competitions.
Asked if his number one striker is at his best, however, Pellegrini responded at his press conference with a flat 'no', before insisting that he match the world's two foremost stars.
'I think he has all the conditions to do that,' he said.
'Sergio is a young player, he has a lot of years to improve - three or four years more than other players. It just depends on what he wants to do in the future.
'I was always sure he would return to his normal performance but I think he can get even better.'