Knight is most notable for playing Dennis Nedry in Jurassic Park and Newman in Seinfeld.
A twitter message posted by the BBC Torchwood account on Monday evening gave us our first clue:
We've got Alexa Havins here with us today with a special guest, here's a clue "uh uh uh didn't say the magic word".
Costumer Alana Stone later tweeted another:
"Dodgson! Dodgson! We've got Dodgson here! See? Nobody cares. Nice hat!"
Both of the clues given are lines said by Knight's character in Jurassic Park.
At the moment the production office has only been releasing clues as to who the special guest is, and it has not been made clear if Wayne Knight was actually on set filming for Torchwood.