The Vale striker, 23, is out of contract, but his age would mean any British club interested in signing him would have to pay a fee.
But with other clubs including Portuguese side Beira Mar also targeting the player, the Potteries club could lose the prolific striker, who hit the back of the net 27 times last season, for nothing.
Meanwhile, Leeds defender Danny Mills could be on his way to Newcastle United. Middlesbrough were favourites to land his signature, however, after Mills hit out at his treatment by Boro, this now seems unlikely.
Also several different sources are still touting the 'Viduka to Boro' story.