The 25-year-old has faced criticism after his reckless tackle during Sunday's Barclays Premier League match at Eastlands left Newcastle forward Hatem Ben Arfa with a broken leg.
De Jong was subsequently dropped from Bert van Marwijk's Holland squad for the Euro 2012 qualifiers against Moldova and Sweden.
"I am very saddened for Ben Arfa - he is an extraordinary player," said Mancini in an interview with Gazzetta dello Sport.
"I hope he returns to play as soon as possible."
He added: "De Jong is forceful but also loyal. He goes hard but not with the intention of hurting anyone. Sunday's episode was just an incident of the game.
"The referee saw it and he didn't even call a foul. I don't wish to enter into the decision made by the Dutch coach. I hope the referees will continue to evaluate De Jong objectively."
Source: PA
Source: PA