The 47-year-old manager remains confident that the Premier League champions will tie up a number of deals on a hectic final day before the transfer window closes
The reigning Premier League champions have had a reasonably quiet transfer window so far, only bringing in midfielder Jack Rodwell from Everton and back-up goalkeeper Richard Wright thus far.
However, Mancini has confessed that the club are working on securing deals for Benfica midfielder Javi Garcia, Swansea winger Scott Sinclair, Fiorentina centre-half Matija Nastasic and Inter full-back Maicon.
"We have another 10-12 hours to close these players," Mancini told reporters.
"We are very close and we are getting closer at the moment and we need more time but I am confident."
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Netherlands international Nigel de Jong has already signed for Italian giants AC Milan on what could be a busy day for the club, and Mancini admitted his disappointment at seeing the battling midfielder leave.
"Nigel only had a one-year contract and this was one of the reasons," he added.
"I am sorry because Nigel was an important player for us but now if he's happy then I am happy for him and I am sure he will do very well in the Italian championship."
Despite his rumoured frustration with football administrator Brian Marwood after missing out on several top targets this summer, the Italian insisted he is satisfied that the club have been working hard to get their business done.
"I was frustrated because it's difficult to do everything in one week or 10 days, it is not easy, only for this reason, but now they have been working very well the last 10 days, two weeks," he continued.