One of the more curious pieces of transfer business last summer saw City snap up England international Hargreaves following his release by their arch-rivals Manchester United.
The Red Devils opted to sever ties with the 31-year-old after seeing a string of serious injuries bring his career grinding to a halt.
City were prepared to take a calculated risk on acquiring his services, with it hoped that he could be a useful addition to their ranks if they could get him fit and firing on all cylinders.
Hargreaves has been able to make four appearances for the Blues this season, but he is currently out of contention and is not expected to be offered fresh terms when his one-year deal comes to an end.
Mancini would welcome the opportunity to select the former Bayern Munich man before the end of the current campaign, but he has been forced to concede that things have not worked out as planned for either party.
"We took a gamble on Owen because he was such a fantastic player," the City manager said.
"We thought we could try to get him fit in two or three months and then he would be able to play. But it hasn't worked out quite like that.
"When you have a player who hasn't played for two years and he starts to train every day there are small problems all the time. Problems in the knees or the hamstrings. So Owen hasn't been able to play when we have needed him.
"He may play again this season but he is not ready now. I hope eventually he will be able to play all the time. He deserves to, because he is a really nice guy."
With Hargreaves currently unavailable, City have drafted in David Pizarro as midfield cover and Mancini is looking forward to working with a player he knows well from their time together at Inter Milan.
"David is not a gamble, he's a top player," Mancini, whose table-topping side play host to Fulham on Saturday, said of the Chile international.
"He can play as defensive midfielder or he can play in the Yaya Toure position. We need cover at the moment because we have players away in Africa, and also because when the Europa League starts we will be back to playing every three days."