The Tigers have had a £6million bid for the 21-year-old accepted but has still not agreed personal terms with the youngster.
“We have to convince him coming to Hull City is the best thing for his career,” Duffen told the Hull Daily Mail.
“I believe the next step for Fraizer is to be at Hull City, where he’ll get a start every week and the opportunity to score goals in the Premier League. That’s what he needs next on his CV, in my opinion.”
“I hope that his previous spell here has some resonance with Fraizer, but like any young professional footballer, he will have ambitions which are his ultimate goal,” he added.
“You don’t go from the start to your ultimate goal in one step and you need to take many steps on that path.”