Mancini insists that the club need to press ahead as soon as possible with transfers in order to avoid missing out on top targets.
The Italian was left frustrated in the two previous transfer windows, but is confident that City will sign their preferred targets this time.
"It is difficult in January to find really good players for us," said Mancini.
"Club's don't want to sell now, maybe they will in the summer. We need to work now, so that it is not like last year.
"I have meetings with Txiki [Begiristain, director of football] every week and we talk about the summer. It will be easier to get players in the summer if we work hard, well and quickly now."
Mancini is currently preparing his side to face Liverpool this afternoon.