The 27 year old is rumoured to keen to leave Vicarage Road with only a year left on his contract and refuses to extend his current deal.
This has prompted both the Blades and Black Cats to make a bid which have so far been rejected. It is also believed that Leeds and Stoke are interested in the hit-man who netted 20 goals last season.
However Neil Warnock has since made a statement suggesting that he would not pay over the odds for the Icelandic International.
He said: "People will only be coming here if the circumstances are right for us and people will only be leaving if the circumstances are right for everyone concerned.
"We've spent some money but we are still doing things sensibly and that won't change," he told the club's official website.