He said: "Fulham concede a lot of goals, and I am an Italian manager. For us Italians it is important to maintain the clean sheet.
"For us, when you are to play in the defensive way, it is from the strikers, it is important everybody is involved.
"It is the same when you try to score goals.You look at Liverpool [in their 3-0 win over Fulham], their first goal was from the goalkeeper, a long pass and goal. Everybody must be involved in this job."
Ranieri replaced Jokanovic, who he made his first signing when he was Chelsea manager in 2000. The veteran Italian praised the Serbian for his work with Fulham, who he got promoted via the play-offs last season.
He said: "Joka was a fantastic player, and in his start as manager has done very good things. I think he did fantastic things here, but that is our life as a manager.
"When something goes badly, you have to change. It happened to me at Leicester, and not only Leicester, that is normal."