Dundee United will look for a fee of at least £3m for striker Nadir Ciftci, who has been watched by several clubs.
Representatives of Charlton, Huddersfield and Norwich watched the forward face St Johnstone on Saturday.
Celtic have also been linked with the Turk and his team-mate Stuart Armstrong, who is also 22.
"It's all speculation at the moment, but we set the bar in summer for sales from this club," said United chairman Stephen Thompson.
Debt-free United are in no rush to sell either player, nor are they under any financial pressure to do so, with Gauld and Robertson having moved to Sporting Lisbon and Hull City, respectively, in the summer.
Thompson added that he had received no bids at this stage for any United players, but that could change once the January transfer window opens.