N'Golo Kante has been heavily linked with a move away from Leicester this summer
Ranieri is desperate to avoid uncertainty about Kante dragging on deep into pre-season with Chelsea among the clubs keen to prise the Frenchman away.
The Italian is confident of keeping key playmaker Riyad Mahrez but is less sure about Kante.
He and Kante have been given extra time off after playing at Euro 2016, but Ranieri says Vardy's new contract has already boosted the squad.
"It is unbelievable," said Ranieri. "It was fantastic because Jamie is our point of reference, or one of our points of reference. Of course all his team-mates are happy and gave us a lot of energy to have another good season."
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