I don't want Marlon to go anywhere," Boothroyd told the Watford Observer.
"You don't get rid of your best players unless you're offered ridiculous money.
"Marlon is one of our best players and I'll fight tooth and nail to keep him.
"We are, and always will be, a selling club because we can't compete with Manchester United or Chelsea but we will do all we can to keep our best players."