The Foxes face Manchester United in the Community Shield at Wembley on Sunday, three months on from their shock Premier League title win.
They are only seventh favourites to win the league this season - at 33-1 - after being 5,000-1 and one of the tips to be relegated at the start of the last campaign.
United appointed Jose Mourinho as boss in May while Manchester City now have Pep Guardiola in charge, Antonio Conte is the new Chelsea manager and Jurgen Klopp heads into his first full season with Liverpool.
Ranieri expects last season's runners-up Arsenal and third-placed Tottenham to challenge again and is wary of the chasing pack.
"Now there are six big teams who want to win, they want to kill us," he said
"That is normal, it's football, but I don't want my players to ever give up against them or anybody
We can lose but I want to see them playing together as a team, helping each other
Suffer for your team-mates, help your team.
"I know last season we did something that is hard to repeat, but I want the maximum from myself and everybody.
"We know very well we are the champions but we are the underdogs
If you are not 100 per cent, give me a 100 per cent of your 60 per cent, then I am happy."
New signings Ahmed Musa, Papy Mendy, Luis Hernandez, Ron-Robert Zieler and Bartosz Kapustka are all expected to be in the squad to face United, while Jamie Vardy will wear a protective cast for the next few weeks following an operation on his wrist this summer.
Leicester lost N'Golo Kante in a £30million deal to Chelsea last month with Mendy, who joined from Nice, his expected midfield replacement, but Ranieri admitted he is yet to discover how they will cope without the France international.
He said: "It's difficult to say how big the hole is
It was the same last season when we lost (Esteban) Cambiasso
We also lost Matty James (to injury).
"They were the two normal midfielders and we lost both
We found the solution
Now we have to restart and watch how we manage to play without Kante
We are okay here
I'm very happy with this team."
Zlatan Ibrahimovic could also make his United debut against the Foxes and Ranieri expects the Swede to be a hit following his free transfer from Paris St Germain.
"Yes, I think so
He's a big champion, fantastic character, a brilliant player and a good player for United," the Italian added.
Source : PA
Source: PA