Janmaat recognises they're rank outsiders going into the game.
But he says: "They win almost every game with a huge domination of possession, Manchester City are going to be champions," said the Dutchman.
"Maybe they have a bad day, we have to go there to get a result, if you do not believe that, you better stay home."
Watford is currently tenth and Janmaat is happy with that.
"Hopefully we can stay in the top half, the main goal is to stay up."