Following their relegation last season, the Hornets are keen to get back into the Premier League as soon as possible, and Boothroyd recognises that they won't achieve this without their top players.
"I do not want Marlon to go anywhere," said the Watford boss of the goalscorer, who missed most of last season's Premiership adventure through injury. "He is the talisman of this club and he knows how much I want him to stay."
"It would take an exceptional offer of silly money for us even to consider letting Marlon go. He is an important part of our plans for the future. We are looking to strengthen the squad this month, not weaken it."