Mangala is poised to start in Tuesday's game against Leicester City in place of injured captain Vincent Kompany, who hobbled off with a calf injury after his brief second-half appearance in Saturday's 4-1 win over Sunderland.
"He (Mangala) is going to be a great defender one day," Sagna told British media. "We just have to be patient. He did well against Sunderland, he demonstrated he can be decisive defensively.
"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.
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"The big difference between him and myself was that he was bought for quite a lot of money, so people will expect him to be above everyone."
The 24-year-old Frenchman was involved in a defensive slip-up which led to the second goal in City's 2-1 loss to Arsenal last week but Sagna said Mangala was trying hard to get better.
"Now we have a setback with him but he started the season very well and we did not concede any goals," Sagna said. "But when times are a bit harder, the first ones to blame are the defenders.
"He is working really hard. I stay with him after training, to work on his position and control of the ball, and he is doing quite a lot to make a difference."
A win against Leicester would ensure the two-time league winners finish in second place at the end of the year, ahead of their opponents on goal difference.
"We have to focus on us, on the way we want to defend (against Leicester), how we want to communicate with each other," Sagna added.
"We want to dictate the game. We want to show we are City and we want to be successful this season."
(Reporting by Nayan Das in Bengaluru; editing by Sudipto Ganguly)
