The Italian has spent more than £100 million during the transfer window this summer, attracting the likes of David Silva, Yaya Toure and Mario Balotelli to Eastlands.
But when asked whether Milner would be City's final summer arrival, Mancini told Sky Sports News: "I think so."
After facing criticism from Sir Alex Ferguson over his summer spending, Mancini responded by suggesting that the United boss has spent his fair share of money in the past.
"If you want to buy a new player you must spend money. It is the market.
"I respect his [Ferguson's] opinion but Manchester United, not Manchester City spent a lot of money in the past."
Although new signing Milner will sit out Thursday's Europa League qualifier against Timisoara, the midfielder could be in line to make his debut against Liverpool on Monday.
Mancini is hoping that the futures of three of his players will be resolved by then, with Robinho, Roque Santa Cruz and Shay Given all linked with a move away from the club, although Mancini is keen for the trio to stay.
"If Shay wants to stay I am happy, if Robinho wants to stay I am happy, if Roque wants to stay I am happy," he said.