Boro want Viduka but any deal is complicated due to the fact that the Aussie is 'leased' to Leeds and because of image rights in his existing deal.
Boro boss Steve McClaren said: "Everybody knows we are in search of a striker and we have made no secret of that, while Mark Viduka is someone who interests us. He is very good player and someone I would love to see at Middlesbrough.
"We've spoken to Leeds and made an enquiry, but it's going to be difficult because at 5pm on Monday, the transfer deadline finishes. Mark is still in Australia, so it seems highly unlikely we will get him at the moment."