Duff has been linked with the head coach role at Oakwell with reports in Gloucestershire suggesting that the Reds have been granted permission to speak with the 44-year-old after making an official approach.
It is understood that Duff is among a group of potential contenders for the position, but the search is far from finalised yet.
The Reds hierarchy are busy sounding out several candidates ahead of finalising a shortlist and embarking on a formal interviewing process and are intent on the process being thorough.
A number of names have been linked with the post, including Burton Albion manager Jimmy Floyd-Hasselbaink, under-23 coach Martin Devaney, who led the side on a caretaker basis following Poya Asbaghi’s departure, former head coach Daniel Stendel and Mechelen chief Wouter Vrancken.
Barnsley saw an approach to speak with Belgian-born Vrancken rebuffed in November.
Reds defender Aapo Halme is set to be released by the Reds this weekend.
The club’s retained list is due out and the former Leeds United player, who has endured an injury-hit time at the club, is out of contract.
Midfielder Romal Palmer and forward Victor Adeboyejo are also out of contract and decisions will be made regarding their futures.
A number of leading players including the likes of Michal Helik, Callum Styles, Brad Collins and Carlton Morris are being tipped to move on during the summer as the Reds face a shortfall of £6-£7m following relegation to League One.
Academy players Jordan Helliwell, David Bremang and Charlie Winfield signed new contracts earlier this week.