Ryan Seacrest has fronted the Fox competition since its first series in 2002, and will return for a 12th run in tonight's premiere (January 16).
When asked by TMZ if Seacrest was considered dispensable like the show's judges, Lythgoe said: "Ryan Seacrest drives the entire programme.
"He's not on an earpiece or anything. He's not beholden to anybody. He controls the show. He's really important."
He added: "It would be very, very difficult to replace Ryan Seacrest."
However, Lythgoe added that American Idol was bigger than any one person, saying: "I've never believed that Idol as a franchise is beholden to any individual because everybody said it would die the minute Simon Cowell left, and it hasn't."
Nigel Lythgoe recently said that American Idol works well because it doesn't rely on "gimmicks".
The new season of American Idol starts with a two-night premiere on Wednesday and Thursday (January 16 and 17) on Fox. UK viewers will be able to watch the new season on 5* when the first episode debuts at 8pm on Thursday, January 17.