The Dutch midfielder still has 18 months left before his reported £90,000-a-week deal runs out, however talks to extend it began over a year ago.
It was reported that negotiations broke down last summer because De Jong felt under-valued and wanted to be amongst the club's higher earners such as Carlos Tevez and Yaya Toure.
Mancini is eager for the future of his star defensive midfielder to be resolved sooner rather than later.
"Nigel is continuing to talk about his contract with the club," Mancini told the Manchester Evening News.
"I hope that we can close a deal, but I don't know when."
The Italian is also keen to get De Jong back into his starting line-up with the 26-year-old having been sidelined since August with a bruised foot.
De Jong did make a return as a substitute for City during their Champions League defeat against Bayern Munich, but has since only been unused from the bench on three occasions for both club and country.
"Nigel is an important player for us," added Mancini. "He had a big problem because he had a big injury for 40 days.
"Now he is OK, and I hope we can close this deal with Nigel - in the next week, in the next month, I don't know - but Nigel has two years left on his contract."