Jagielka will return after being absent since late February, but despite his captain regaining full fitness, Martinez has revealed that the England international isn't guaranteed to play against Manuel Pellegrini's team.
The 40-year-old told reporters: "He is fully fit for Saturday and that has always been the plan, to get him fit for the Man City game.
"He is fully fit but to play 90 minutes, it needs to be my decision depending on the players. It's just a team decision.
"He is fit, medically fit, but that does not mean that he is going to get a place. Nobody has a place guaranteed in the team, not even the skipper."
Jagielka has made 28 appearances for the Toffees during this campaign.