The City manager is baffled that Barcelona and Real Madrid overlooked the gifted midfielder, signed from Valencia in 2009, who has played a dominant role in the club's 100% start to the season.
Mancini said: "Silva is a top, top player. I don't know why he didn't go to Barca or Real Madrid because he's Spanish but we are lucky because he's here."
He added: "If he had gone to Barca two years ago everyone would say he's one of the best players in the world - and he is one of the best players in the world.
"He's different from Messi and Cristiano Ronaldo because they are strikers and score a lot of goals but I think he's the same as Xavi and Iniesta."
City will make their debut in the Champions League on Wednesday when Napoli come to Manchester, and Mancini will hope to reap the dividends of a rotation policy that is one of the benefits of his large and talented squad.
Mancini admits the players may not be happy to kick their heels on the bench - for example Edin Dzeko did not play a minute of City's 3-0 win over Wigan at the weekend despite scoring four goals in the previous match.
Mancini said: "They may not be happy - that's impossible because every player wants to play always, but I'm the manager and I need to take this decision.
"Now we have a difficult match coming up, we play every three days and these players like Edin, Kolarov, (Stefan) Savic and (Samir) Nasri have played two games in four days and they need to recover.
"We have a long year and I need all the players to be available as much as possible and sometimes it's better that they rest. We have the first game in the Champions League for the club, it will be an exciting night but we need to have a focus and make sure we beat them."
Source: PA
Source: PA