The Italian manager has been told that City cannot afford to continue spending big money in the transfer window.
The club revealed that they posted losses of £195m in their last annual financial figures. The new transfer policy is a direct consequence of the Abu Dhabi-owned club trying to fall into line with UEFA's financial fair-play rules.
"We need to sell two or three players and then we'll see," said Mancini.
"We want to sell first and after that we may have time to buy someone if it's possible. But it's not easy.
"There are players that could be good for us but every time we want to buy a player their clubs ask for lots of money."
City face West Brom today at the Hawthorns.