Celtic are Duffy’s preferred choice as he grew up supporting the club in his native Ireland.
West Ham United and West Bromwich Albion do offer some competition, however, and Wednesday’s Champions League elimination could impact any potential deal.
Reaching the group stages would have given Celtic a financial boost, but he will now join the Europa League.
According to The Athletic, this elimination appears to be a setback in their hopes of landing Duffy.
However, the website also reports that Brighton is keen to help the center-back get the move he wants.
Duffy is popular with the staff and his teammates and while all decisions also take into account what is best for Brighton, they want the defender to leave on good terms.
There is no room for the Irishman at the Amex, Ben White is set to follow Lewis Dunk by signing a new deal with the Seagulls.