Clark has played in a number of roles for the club, including full-back and central midfield.
But Lambert has been impressed with Clark since using the Republic of Ireland international at the heart of Villa's defence.
He said: "What is Clark's best position? My own view is that he's a centre-half. That's where I think his strength is.
"We might have to use him somewhere else if we get injuries but at this moment in time I see him as centre-half.
"He has been excellent for us. You're placing a lot of responsibility on him and he's been thriving with it."