The Blues head into Sunday's Community Shield showdown with Chelsea at Villa Park still to make their first signing of the summer. One transfer target, Eden Hazard, will be in the opposition ranks, whilst a second, Robin van Persie, looks to be bound for Manchester United.
Mancini is still hoping to secure the services of Daniel Agger and Daniele de Rossi before the new campaign begins against Southampton on August 19. However, the Italian said: "When you win something it is important to improve. But you should not buy new players 10 days from the end of the window. It should be two months."
"The championship finished on May 13. You needed to buy players before now. Now it is difficult because there are some teams who can't sell their players because they don't have time to buy anyone else. The next 20 days is very difficult in the market."
Mancini has expressed his frustrations with sporting director Brian Marwood. Yet the situation is not as straightforward as the Italian would like to believe.
It is fairly obvious City have the finances to fund any deal. However, Marwood is having to juggle the demands of meeting UEFA's Financial Fair Play regulations.
That is already going to be difficult given the vast sums City have spent. But with high earners like Emmanuel Adebayor proving hard to shift, Marwood will not sanction further outlay.
It is why United are set to profit from the arrival of Van Persie, which Mancini believes will only make the Red Devils stronger.
"If United buy Van Persie it is better for them," said Mancini. "They need a player like Van Persie. He could play for any team because he is a top player."
So good in fact that Mancini feels United are favourites to win the title this term, with his team as low as fourth. "United start as favourites this year," said Mancini. "We are maybe in second, third or fourth position."