The Barclays Premier League champions currently trail neighbours Manchester United by 15 points and retaining their title looks a distant hope.
That appeared to put pressure on Mancini's future but Soriano, who moved to the Etihad Stadium from Barcelona in the summer, has a greater understanding of the situation.
"It is not easy to win back any league, especially the Premier League," he told a press conference in Italy where he was picking up an award for his book, Goal: The Ball Doesn't Go in By Chance.
"One year you can win with luck but in the long term you need planning and investments to reach the final of the Champions League.
"In 2003 we did a study at Barcelona and for every player who ended up in the first team from the academy there was an average cost of £2million, which is nothing if you think of the current cost of players.
"The principle of bringing players through is fundamental to give a technical identity to a club, because that leads to a style of play.
"They have to learn from five years old the style of the team, and then you get the benefits."
City's rise to Premier League champions was built on a massive spending spree but Soriano insists that will not be the case moving forward.
"Our squad is still competitive. Our problem is finding players stronger than those we already have and that's not easy," he added. "In the last three years, we have lost £200m, then £100m and now we're on track to be in the red by £50m, but we have also invested £150m in youth structures. It is a fantastic project, aimed at financial sustainability."
- Sports & Recreation