The champions are just two points above the relegation zone only seven months after winning the Premier League in one of sport's biggest shocks
They lost 5-0 in their final Champions League Group G game in Porto on Wednesday, having already qualified for the last 16, and now have a break from Europe until February with the draw for the second round made on Monday
Leicester host Manchester City on Saturday and Ranieri is keen to focus on their league problems now they can forget the distraction of Europe
He said: "This part of the season is our key moment
"The players aren't satisfied, they want to play better and fight more but it's important to fight together as a team
Our strength was this, if we made a dream last season it's because we were together, not because we were a big team
With our effort we made a story.
"Do you see the same team from last season? I don't see, we have to react, to come back.
"The recruitment area are working hard but they wait for me to say 'Okay, now i need this, this and this
Until then I want to check my players and the only players who will stay with me are the ones who want to fight until the end."
Leicester have not won in the top flight since beating Crystal Palace 3-1 in October, their only victory in their last eight league games.
Pep Guardiola's Manchester City have won just four of their last 14 games and have slipped to fourth in the Premier League, four points behind leaders Chelsea
Sergio Aguero is banned this weekend but Ranieri knows City have talent in abundance
"There are so many champions, there is Kevin De Bruyne, there is David Silva, there is Kelechi Iheanacho, there are so many," said Ranieri
"It is a big team, fantastic players, but I want to see (them) against us, when we are strong."
Jamie Vardy, Riyad Mahrez, Robert Huth, Andy King and Islam Slimani will all return after being rested for the trip to Porto.
Source : PA