Rodwell was a £12m signing last summer from Everton but he has not played since suffering the latest in a series of hamstring injuries on England U21 duty in October.
The 22-year-old had hoped to be back before Christmas but suffered another setback and is now unlikely to return before the final week of January.
His time at Goodison Park was also blighted by injury which ruled him out of Euro 2012 and the Olympic Games, but Mancini feels he is young enough to still go on and prove he was right to sign him.
"We hope we can improve this situation for him," Mancini said. "He is young and he has quality - he has everything to be a good midfielder.
"I worry because when we bought him we thought he was a good player and then he had these problems with hamstrings.
"He is getting better and we hope we can recover him in two or three weeks. He needs to start working with the group and he didn't do this until Thursday."