The 28-year-old Republic of Ireland international winger is gradually working his way back to fitness after damaging ankle ligaments in April.
The Magpies manager told the Journal: "There are not many better wide players in the Premier League than Damien Duff, and it is up to us to get him back to the level he was a couple of years ago.
"If he is playing to his full potential, he would be an asset to any club in the Premier League. He was a wonderful player at Blackburn and Chelsea and he wants to show people what he is capable of at Newcastle.
"He had a frustrating time last season with injury and he wants to show people the real Damien Duff. He has been working extremely hard, but the injury he had was a career-threatening one. It was a really nasty injury. It has been a long and difficult recovery for him, but he is desperate to get back."