Conan O'Brien has turned down a guest slot on 'American Idol' because it clashes with the termination agreement he signed with NBC.

American Idol asked the comedian to take par tin their April 21 'Idol gives Back' special but O'Brien had to refuse because of his termination deal.

He is not allowed to make TV appearances until May 1st.

O'Brien kicks of his legally Prohibited" show in Eugene Oregon on April 12th but it is expected that at some point Fox will sit down with him and discuss whether he can be part of their late night line up.

O'Brien is comfortable with Fox having started work there with 'The Simpsons'