De Rossi has been touted as a potential City purchase for some time.
And, with Mancini concerned about his options when Yaya Toure departs for the African Nations Cup next month, there had been suggestions City would make a move for the 27-year-old Roma man but Mancini concedes he may need to bring in reinforcements, he doubts whether De Rossi can be prised away from the Italian capital.
"I don't think so," he said. "De Rossi was born in Rome and it's unlikely that he'll leave the city. 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."
And that creates a problem. Not so much with the cost - Sheikh Mansour has pockets deep enough to sign any superstar who becomes available - but with UEFA's Financial Fair Play structures.
It means City have to start unloading some of the men they no longer need.
Negotiations with AC Milan over an exit for Carlos Tevez have already begun, although they may become protracted.
Mancini has already questioned why Wayne Bridge prefers to remain surplus to requirements when there are clubs of a decent size - Celtic have been mentioned - who would like to sign him.
And former England Under-21 international Nedum Onuoha is another player with senior experience who has no future at the Etihad Stadium.
"We need to sell two or three players and then we'll see," Mancini said. "Until now we have been lucky because we haven't had any big injuries. I hope it can be like that in January but if not, we may have time to buy someone. It's not easy though. I asked the owner for [Lionel] Messi but it's not possible."
Source: PA
Source: PA