The 29-year-old, clearly feeling the benefit of a rare injury-free pre-season, was in sparkling form against Hartlepool over the weekend and was rewarded with a well-taken hat-trick.
"He is at the weight he was when he was 18 and he has worked so hard in training, the running and the way he has worked with everything we have put on probably showed out there on Saturday.
"After 70, 80 minutes, he still looked like he had got a turbo-charger in him, as did James Milner and a couple of the others.
"You have just got a draw a line under where he has been and just judge him from now, now he has had a chance to put a foundation into his season, which he hasn't had for three years.
"Any players who misses the pre-season, you ask any player, no matter how good they are, where they have played and what qualities they possess, it is very hard without that base.
"I think you will see a different Damien Duff this season. There were signs of that on Saturday, but obviously, there is more to come."