Mancini insists City must spend big this year if they are to mount a sustained challenge next term.
"I don't know how much money we can spend in the summer, but in the past United spent a lot of money to buy important players and now they don't need to spend £100million every year.
"United are a top team. Now they just need to buy one top player every year because they are strong.
"For us it is different. We need to do it this way now and, may be in the next three or four years after that, we would only need to buy one player every summer because we have a strong team.
"I repeat that we are not like United.
"They have a big history and we need a lot of years to compete with this.
"We need to improve our team every year and this summer we need to buy the players who can make the difference, important players that can improve our team and make us better."