The actor told TV Choice that an enemy from the show's original 1963-1989 run might make an appearance in a future episode.
"Perhaps there are some classic monsters coming back," he teased. "There's one I'm very intrigued by, which we haven't seen for quite some time."
Quizzed about the returning threat, Smith clarified: "[It's] a thing we haven't seen since the series returned to our screens in 2005."
Classic monsters the Daleks will reappear in the Doctor Who series seven premiere, penned by Steven Moffat, which airs in both the UK and US this Saturday (September 1).
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Watch the stars of Doctor Who discuss series seven and the 50th anniversary with Digital Spy below: