Rob Burnett spoke to Entertainment Weekly after Letterman implied on-air on Thursday that he saw himself continuing to host the show for 'a couple of years'.
Burnett said: "It was kind of a tossed-off response. I think it's a response [that] he's given multiple times.
"In no way was last night's show any kind of actual announcement... I think when a guy ends a 30-plus [year] career on television, it's not going to be guessing about whether he's leaving or not. It won't be ambiguous.”
Letterman's contract is thought to expire in 2012.
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