"Nothing is impossible, but it's not something we're particularly striving for," he explained. "There's enough inevitable crossover talk between those two, [so] it might be disconcerting for either of [Matt or Benedict Cumberbatch] to appear in the other's show."
The writer added that he would only cast Smith in Sherlock if there was "a perfect part for him".
"Stunt casting doesn't work, so it would have to be just because he was overwhelmingly right for it," Moffat continued.
"I love working with Matt. He's a phenomenal actor. I'd jump at the chance to work with him again. I [just] don't know how likely that is to be on the set of Sherlock.'"