Mangala was a whopping £32million purchase for City from Porto at the start of last season but the defender has not come close to justifying his price tag during his time at the Etihad Stadium so far.
Nonetheless, Mangala has shown signs of his quality this season and defensive colleague Sagna has now gone on to back his fellow Frenchman to come good sooner than later.
Sagna said: "Of course it's never easy to take criticism, but Eliaquim is still young. The club bought him for a lot of money and it's not easy to deal with it because he is always going to have that image, that he's the most expensive defender. But he is working really hard.
"I stay with him after training, to work on his positioning and control of the ball and he's doing a lot to make a difference. He wants to get better and I want to help him. We try to communicate, even after games, we try to analyse when we concede goals what he should have done better, what I should have done better.
"Most of the time you forget he only came last season to this league. This league is difficult, especially when you come from abroad you need time to adapt. I think he is doing quite well.
"He's going to be a great defender one day. Now we just have to be patient. He did well against Sunderland on Saturday, he demonstrated he can be decisive defensively. I think it's just about confidence. He's still only 24 and he's going to improve a lot.
"I want to remind everyone that to come and play in this league is not easy at all. I had a chance to come to Arsenal and it was different for me. I came at the same age, 24, and from the first season I had, everything went well."