City, the Barclays Premier League leaders, are reluctant to spend on players this January as they try to keep their outgoings down ahead of UEFA's new financial fair play rules coming into force.
Asked if he had been told he couldn't buy this month, Mancini said: "Yeh, yeh. This is the problem. But if we don't have the players it's tough for us. We are not United. The difference is this. United and Chelsea have won trophies for many years. So they are quiet now. They understand that they can play without pressure.
"For us it's different. This could be the first championship for many years and we need to do everything we can to win it."