The Foxes were top of the league at Christmas but have slipped to second, two points behind Arsenal, and are goalless in their last three games after losing 1-0 to Liverpool and drawing 0-0 with Manchester City and Bournemouth.
Italian Ranieri has spoken all season about the need to secure 40 points -- the tally deemed sufficient to ensure Premier League survival -- but is worried his players will ease up now after reaching the total.
"If they lose impetus I will be very furious and desperate. If someone loses this focus, they are out," Ranieri told reporters.
"We want to win. I saw them after Manchester City, Manchester United and Bournemouth and they were very sad -- and that is good."
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Leicester were bottom of the league last season before fighting back with seven wins in their last nine matches to escape relegation.
"Now we are doing something that nobody could have expected. The owner asked me to have 24 points at this moment. We have 40. Fantastic," added Ranieri.
Striker Jamie Vardy, the division's joint top-scorer on 15 goals alongside Everton's Romelu Lukaku, has shrugged off the illness which has hampered him in recent games and is likely to return from a minor groin operation for Wednesday's Premier League match against Tottenham Hotspur.
The Foxes also take on Tottenham at White Hart Lane in the FA Cup third round on Sunday.
(Reporting by Rob Hodgetts, editing by Pritha Sarkar)
