Duffy always knew that McClean had talent, but admits to being taken aback by the speed to which he has adapted to Premier League life.
"He was a good player when I was growing up with him and he's a few years older than me, but I still think that he's surprised everyone.
"When you see him now, you couldn't believe that he's come from Derry and the League of Ireland. It's all credit to him. He's a top lad."