Hull City and Ipswich Town are also eyeing a move for the Crystal Palace striker.
The striker is free to leave Selhurst Park this month, with manager Alan Pardew looking to bring in another forward in the January transfer window.
Palace are prepared to allow the striker to leave on loan, but are determined to receive a big fee from whichever club takes him on board.
He would be a smart signing for all of those sides, having managed 15 goals while on loan in the division with the Tigers in 2007/2008, and also bagging 15 goals while at Cardiff City in 2013/14.
Of the four sides interested, QPR and Wolves are both in the most need of a new forward, having lost Charlie Austin and Benik Afobe to Southampton and Bournemouth this month and will likely be at the front of the queue.