King has made a big impact at Vicarage Road since joining Watford on loan from Forest in the summer, a move that has now been made permanent and is currently the top scorer in the Championship.
He was however left out of the starting line-up for Saturday's game at Reading, sparking talk of a bust-up with Boothroyd.
The Hornets boss however said: "The rumours aren't true at all. I don't tend to have rows with people. Any player is disappointed when he is left out of the starting line-up.
"Marlon wants to play, but I think he respects me and he gets on with it - as do all the players."