Speaking to the CT about King's 59th minute dismissal, Boothroyd said: "Marlon gives everything in a game and sometimes he tries a little too hard which is what happened here.
"It was a typical strikers tackle - over exuberance, nothing malicious - and the lad's thrown in a couple of rolls and a triple salchow to make the most of it,
"But like Aron Gunnarsson's tackle against Norwich, Marlon had two feet off the ground and that's an automatic red. There's no point in appealing because that is the letter of the law so Marlon will miss the games against Barnsley, Palace and Sheffield United but he's got to take that on the chin.
"Marlon's very disappointed, because there was clearly no intent to hurt the player. There was a tackle in the game where there was some intent and Lee Carsley is lucky to escape with both his legs intact but sometimes they get seen, sometimes they don't.
"You just hope they even themselves out, so I'm looking forward to a really uneven run of decisions in our favour for for the rest of the season.