King's signing on Monday saw one of the most protracted chapters in the club's history and was one that was made to happen by Boothroyd's determination to get someone he believes in, playing for him.
King replaced Carl Baker in the 52nd minute of City's 2-1 defeat and impressed the City boss who told the Press Association: "Marlon did well.
"He hit the target with his shots and the crowd responded well to him which was nice, but we didn't expect anything else.
"He has given himself a good chance of starting on Tuesday. He's focused and very much looking forward to playing a key part in what we are doing here."