No 'guarantees' that Callum Styles and Michal Helik will be sold by Barnsley FC after turning down bids
So far this summer, the club have sold Cauley Woodrow and Carlton Morris to Luton Town and Callum Brittain - with the sale of leading players helping to bridge a shortfall of between £7m and £8m following relegation.
Styles is on the radar of several Championship clubs and others on the continent, including Greek outfit Olympiacos and Turkish side Besiktas – managed by former Reds chief Valerien Ismael.
Polish outfit Lech Poznan are among those keen on Helik.
The Poland international came on as a substitute in the 2-1 friendly win over Sheffield United on Saturday. Hungarian international Styles started the game.
Duff, speaking to BBC Radio Sheffield, said: "We have turned down bids (for Styles and Helik), but it is the sign of having good players.
"If you have got good players, other clubs want them. We want to keep our best players and then there's the trade-off in the transfer market where two clubs agree that is the going rate.
"That is where we are at, at the minute. The pleasing thing from my point of view is that when I did walk through the door and there wasn't a fire-sale immediately.
"I hear all the same information as you that he will be gone, he will be gone and he will be gone. That's not to say they won't go, but there's no guarantees that they will go either.
"With actual bids, it's not for me to say where they have come from and not fair. We've turned down bids for them."
Back in June, Reds chairman Neerav Parekh admitted that the summer would be a challenging time for the club, financially, but also insisted that players would not be sold on the cheap either.
To help the club's running costs in the first part of the summer, a cash boost of £1m was put in by investors and Parekh did not rule out another injection if needs be.
Speaking at the time, he said: “The £1m will be used for everything typically that revenue coming into the club is used for. Paying wages, recruiting players over the summer and the general running costs of the club.
“There is a financial hit (from relegation). No doubt about that and no way to sugar-coat that. But if there is a further need for capital, the board will make the call and see if we need to put it (more) in.
“I also do not want to hide away from the fact that we are going to sell players (eventually) to bridge the shortfall.
“Part of the reason to put the money in early was to make sure we did not have to sell the players with the first offer that came in.
“If we get a reasonable offer for a player that we think matches the valuation, we will sell. But equally, if we don’t, we will keep the player even if means running down their contract and having them go for free.”