The former Ireland manager was full of praise for the big centre half who emerged as one of the most effective defenders in the English Premier League last season.
Duffy, who was crowned ‘Player of the Season’ at the Seagulls last term, has been linked with a summer move to several top Premiership clubs.
However, O’Neill, who revealed he advised ex-Brighton boss, Chris Hughton to sign him from Blackburn Rovers in 2016, says he must keep grounded and continue doing what he does best.
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“I remember when Chis Hughton was managing down at Brighton and Shane was having a nightmare couple of weeks early on at Blackburn Rovers,” recalled O’Neill. “He scored a couple of own goals.
“Chris phoned me up and asked me about him and I told him ‘Take him all day, take him, absolutely.’ That was great for me and Duffy has gone on to do really, really well.”
And considering his life-threatening injury sustained in training with Ireland in 2010, O’Neill has been hugely impressed with how he’s performed consistently at the top level for both club and country.
“What he wants to do is keep at it. Don’t think he’s made the grade, just keep going. But Duffy was great for me. He scored a big goal against Denmark there again recently - another big header, so well done him
“Considering the problems he’s had, the health problems when his spleen was in bits, it’s excellent so well done him. He’s a good old character.”O’Neill, who was at his alma mater, St Columb’s College in Derry to officially open its new sports centre, was also glowing in his praise of Duffy’s international teammate and fellow Derry man, James McClean.
“James McClean, who I love dearly, has a great heart,” he said. “In the qualifying games for the World Cup I think he took on the mantle and became the big, strong character that he is now. Obviously his goals were very important and he’s really terrific. James has a really big character. He is a really good athlete as well and is physically fit. James has his lunatic moments like everyone else but I love him to death.”
And O’Neill claims young aspiring Derry footballers should follow in his footsteps.
“Derry City in particular has been blessed with talented people for a long, long time. Every single generation. I’ve often felt, maybe as a boarder ( at the College) or looking outwards at the day boys from Derry City, they were very talented lads and talent comes easily to them but you’ve got to have a driving force as well.
"Some of the lads have tried to go over and try to make the grade in England but maybe felt a bit homesick and came back again and lost that will to go back. If you’re really serious about it and you’ve got the talent then I think they shouldn’t take ‘no’ for an answer. I think they should drive on if, indeed that’s what they want to do.”