Sheffield United are the latest English club to admit an interest in Hearts striker Mark de Vries.
Mark de Vries has impressed domestically and in Europe
Hearts have already turned down a bid from QPR and reports have suggested that Plymouth Argyle are prepared to pay £100,000 for the Dutch 29-year-old.
Now United manager Neil Warnock has told his club's website: "Mark is one of the lads we're looking at.
"He is available on a Bosman free next summer, so Hearts might want to do business in the transfer window."
De Vries is one of 12 Tynecastle regulars whose contracts expire at the end of the season.
And speculation has linked Republic of Ireland full-back Alan Maybury with a £30,000 move to Leicester City.
Hearts head coach John Robertson has admitted that English clubs have the financial clout to offer higher wages.
De Vries, who joined Hearts from Dordrecht in 2002, is the prime target after some fine performances in the Uefa Cup.
He netted 16 times as the Edinburgh club finished third last term but has only scored three goals in a season so far blighted by injury.
Robertson had been hoping to hold contract talks with the Dutchman.
"I spoke to Mark and he was quite positive, saying he would be happy to stay if the terms were right," he told the Edinburgh Evening News.
"We will offer Mark the best we can. But we have to be sensible with the money and can't afford to overspend."
Player representative Armand Doorn said last month that De Vries was likely to leave at the end of his contract in the summer unless Hearts give the striker a large pay rise.