The Champions have struggled to reach the heights of last season in the league, with the Foxes 14th ahead of Saturday's game against Sunderland at the Stadium of Light (3pm kick-off).
They have enjoyed far more success in the Champions League, though, with Leicester qualifying for the last 16 with a game to spare.
Ranieri has urged his side, who last won in the league in October, to build on their European success.
"I am confident, but we must work so hard with a strong mentality,” said Ranieri.
The 16 places where most crime was reported across South Tyneside in June
Angry patient trashed doors at South Tyneside District Hospital after falling asleep and missing treatment
Extension plans rejected for South Shields home
‘Sinister’ paedophile watched children play and offered them doughnuts after moving into new neighbourhood
‘It could have been much worse’ – see pictures of fire devastation at Hebburn home
"We have to live in two ways – the Champions League and the Premier League.
"In the Champions League we are so happy, but in the Premier League we aren’t happy. It’s important now to be focused on the Premier League.
"Of course, something has happened.
"The players are human – they are not machines – so it’s normal that they remember that everybody last season played well.
"Everything we did was good, but not this year. Now, we have to reconnect our brains. They must play with pressure.
"They must be focused and play with the same character.
"If you are under pressure, you are very smart, attentive and careful about every breath, but if you are relaxed, it’s not possible."
Leicester rescued a point against Middlesbrough at the King Power Stadium last weekend, with Islam Slimani scoring a late penalty.
Ranieri could have Nampalys Mendy in his squad at the Stadium of Light after the midfielder finally shook off an ankle injury which has sidelined him since August.
He suffered the injury on his full debut against Arsenal but may make the bench along with fellow ankle injury victim Ben Chilwell.
"Everybody's available and they trained very well. It's an important match for them and us and we are ready," said Ranieri.
"Mendy and Chilwell are back training with the first team and they are available.
"Of course they don't have 90 minutes under them but are okay."