The 26-year-old combative Dutchman has not featured for City since the four-goal defeat of Swansea a month ago. It was anticipated De Jong would only be sidelined for a couple of weeks at the most with a bruised foot.
However, as the games have gone by, the former Hamburg midfielder has seemed no closer to re-appearing.
Happily though, it seems his exile is nearing an end and he could even be involved in Tuesday's crucial Champions League encounter with Bayern Munich at the Allianz Arena.
"I don't know what has happened with Nigel," admitted Mancini.
"It was a bruised foot and always when a player has been out for a month or so, I wonder why.
"He is a strong player but he has had pain for four weeks. He started to train two or three times. Every time it hurt and was difficult for him to run.
"But in the last week he has improved a lot, which is good news because he is important for us."
In De Jong's absence, Gareth Barry and Yaya Toure have been occupying the midfield holding role.
Another option emerged on Wednesday when Owen Hargreaves came through almost an hour of his first extended run-out for three years.
But Mancini knows De Jong offers something different, which City need if they are to be successful at the highest level.
"Nigel is different from all our other midfielders," said the Blues chief.
"He works a lot in the middle. He recovers possession.
"When we attack, we can do so with more players because Nigel can stay and help the defenders."
If De Jong does not make it to Munich, when City will look to build on their debut night draw against Napoli, he has been pencilled in to play at Blackburn next Saturday.
His presence not only offers Mancini an additional option, it swells numbers in his squad, which the City chief believes is vital if the Blues are going to make the impact he is looking for in all competitions this season.
"We need to keep our players fit, so we can change them around for all the different games," he said.
"When the FA Cup starts, it is on a Saturday, so that is not a problem.
"Champions League and Carling Cup matches are on Tuesdays and Wednesdays, which is more difficult.
"We will try to go for it in everything, but sometimes we might need to take a little risk."
Source: Team Talk
Source: Team Talk