Considerable speculation inevitably accompanies wealthy City into any transfer window but this time the main movements could be outgoing.
And on the prospect of bringing in new players, the Italian said: "We could maybe bring someone in, but we need to sell."
City are looking to offload absent striker Carlos Tevez while defenders Nedum Onuoha and Wayne Bridge, both surplus to requirements, are also available.
The club have already held negotiations with AC Milan about Tevez but have not yet reached an agreement as their hope is for an immediate sale while the Italians want to loan the player first.
Mancini believes a deal could be done quickly if Milan agree to their terms but he says other clubs are also interested.
He said: "We need to sell three or four players and with Carlos we could close (a deal) with a club in the next three or four days, and also possibly Wayne. Then maybe we can do something."
He added: "We hope for us and for Carlos we can do a deal. There are two or three teams in Italy, a team in France, and another team involved - I hope for him he can start to play football.
City have been linked with Roma star Daniele De Rossi to help cope with the loss of Yaya Toure, who is bound for the African Nations Cup with the Ivory Coast, but Mancini does not know if a deal for his fellow Italian is feasible.
He said: "De Rossi is a top player, like Yaya, but he plays for Roma, a top team, and he was born there. I don't know if he will leave."