Ranieri, who signed Lampard from West Ham for £11 million in 2001, declared: "We are full in midfield and won't be signing anyone else there.
"Frank is a fantastic player - I know that better than anyone - but the only player we need before the start of the season is a central defender."
However, Ranieri is a confirmed admirer of the 28-year-old midfielder.
He said: "Many people said Frank wasn't worth the money when I signed him but he worked very hard and went on to become one of the best midfielders in the world. That made me very proud.
"We had a great relationship when we were at Chelsea and it was good to catch up with him after England's game against Brazil last month."