Leboeuf declared last summer that Chelsea should clear out the Old Guard, which included Lampard.
Leboeuf now says: "I was wrong in my judgement about Frank.
"He is the catalyst in the team. He dictates play, he organises things. Frank is the voice of Di Matteo on the pitch.
"I could not see him becoming that kind of player when I was playing against him while he was at West Ham. He has developed and matured.
"Frank will have a big role for Chelsea this season. There is no doubt in my mind about that.
"My one concern is that he cannot play in every game, and I wonder who will do the same job when he is not there."