The Italian manager has announced that the incoming midfielder is a signing for the future and must get used to competing for trophies as he swaps Everton for the Etihad Stadium
City announced on Sunday that they had agreed a fee with Everton, believed to be around £18 million, to lure the 21-year-old to the Etihad Stadium.
But speaking after City's 3-2 win over Chelsea in the Community Shield at Villa Park, Mancini spoke of the incoming midfielder as a player for the future who must get used to competing for trophies.
"Jack Rodwell is a young player who needs to improve to play at this level," said Mancini. "He's a good player for our future, I hope. I liked Jack last season and for this reason we bought him.
"He's doing a medical at this moment. I think he's a good player, he's young and it's the first time he'll play to win things. It will be difficult for him but I am sure in a couple of years he will be a top midfielder because he's strong."
Rodwell will become the first summer arrival at City following their Premier League title triumph and Mancini admits he remains frustrated by the lack of progress in their pursuit of transfer targets including Arsenal captain Robin van Persie.
"I'm unhappy, it's normal," added the Italian. "Every manager is unhappy if one week from the season they haven't bought any players, but we are working this week.
"We are looking for other players. I'm waiting at this moment and I think tomorrow we will talk about other players."