Ranieri was confirmed as the replacement for the sacked Slavisa Jokanovic on Wednesday, seeing the Italian return to the Premier League for his third spell.
It was in his last stay in England that Ranieri had undoubtedly his greatest impact, as he led unfancied Leicester to the 2015-16 league title, a sporting achievement regarded as one of the greatest in modern times.
He was sacked in February 2017 with Leicester embroiled in a relegation battle, but Fulham owner Shahid Khan was clearly unperturbed and has put Fulham's own survival hopes in the 67-year-old.
Although a time may come to be ambitious, Ranieri told supporters to forget about "miracles".
"We have to work hard," Ranieri told reporters at his presentation media conference. "That [the Leicester title success] was a bonus, a fairytale. We need to forget it.
& suits you Mr Ranieri pic.twitter.com/t5EaGwHEvM— Fulham Football Club (@FulhamFC) November 16, 2018
"I think now it is important to not think about miracles, but think about a lot of battles and be ready together. I repeat; together. The club, the players, the fans – together.
"Together they must support us, and this is a bad moment because we're at the bottom [of the table].
"I am an ambitious man, I have good players, but I choose those that show me fighting spirit.
"When players and fans help each other, [we] understand we are all together in the same way. Now I need the support of our fans to try do our best."
Jokanovic played under Ranieri when he was in charge of Chelsea and the Italian commended the job his predecessor did in getting Fulham promoted last season.
Ranieri, though, added that things can change quickly in football if results are not being achieved – something he experienced with the Foxes.
"Jokanovic was a great player and also starting as a manager he made good things, fantastic things here at Fulham, but this is the life of the manager," Ranieri added.
"When something goes badly, you have to change. It happened to me at Leicester."