The 23-year-old forward scored 18 times for Aberdeen last season and has already registered an assist in two games in the new campaign.
Duk is being linked with a move south of the border where several Championship sides are interested in getting their hands on him.
Four sides were present at Pittodrie to watch Duk in action against Celtic last weekend as they continued their checks with a view to a possible bid.
It has been claimed Leeds and Southampton are two of the clubs who watched the forward feature against the Scottish champions.
Leeds and Southampton are in the market to bring in a striker before the window slams shut on 1st September.
Duk is one of several strikers who are being considered in recruitment meetings at the two clubs.
It remains to be seen whether either of the two clubs make a concrete offer to land the Aberdeen striker in the ongoing transfer window.
