Wolves striker Steven Fletcher has handed in a transfer request as Sunderland stepped up their bid to sign the Scottish international, Press Association Sport understands.
It is believed the Black Cats have tabled a £12million bid for Fletcher with the npower Championship club. But Wolves will have to pay Fletcher's previous club, Burnley, a slice of any transfer deal and are determined to obtain the highest possible price for the player.
Wolves have confirmed Fletcher's request but will not sell the player until the club's valuation of the 25-year-old is met by any interested clubs. A statement from the club read: "Wolves can confirm that Steven Fletcher has handed in an official transfer request."
The statement added: "The player's frustration stems from the fact that several bids have been rejected for his services, none of which meets the club's valuation.
"As previously stated, no player will leave Wolves unless the club's valuation is met.
"Wolves will be making no further comment at this time."
Fletcher joined Wolves in June 2010 from Burnley, signing a four-year contract with an option for a fifth year.
The Scottish international has finished as top goalscorer in both of his seasons at Molineux, reaching double figures in the Barclays Premier League on both occasions.
He made 26 Premier League starts last season, scoring 12 top-flight goals. Fletcher has not played in any of Wolves' pre-season games for the past two weeks because of an ankle injury.
Wolves also sold winger Michael Kightly to Stoke on Tuesday, while defender Christophe Berra asked to leave last week. Liverpool are also interested in goalkeeper Dorus De Vries, who played under Reds boss Brendan Rodgers at Swansea.