Many Premier League clubs would look at City's capture of Aguero in 2011 as a missed opportunity.
At the time, then captain Terry wanted David Villa rather than Aguero. He said back then: "I think we'll see Chelsea back and competing for the top players who are out there at the moment. The likes of Franck Ribery, David Villa. These are the kind of players we want to attract.
"Valencia are struggling for money, that's well publicised when it comes to Villa, and there's been a lot of talk about Ribery. We'll be in for players in the summer, but when big players like them become available, we need to show people that, yes, Chelsea are back.
"There needs to be a couple of changes, a few players brought in and a few who haven't played in the last couple of years moved on. As players, we've said our feelings about what we feel needs to be improved. Hopefully Roman will listen and things will get done."
Their manager Carlo Ancelotti wanted Aguero a year later, but the club did not make a high enough offer to tempt Atletico.
Eventually, Aguero went to City, where he went on to score 244 goals in 353 appearances and counting.