The Scotland forward moved to The Hawthorns last summer in a £1.25million deal from Celtic - but failed to cement a regular first-team spot.
The 24-year-old fell behind Kevin Phillips, Roman Bednar and Ishmael Miller in the striker pecking order - and was sent to Deepdale on loan in March.
The Preston gaffer told the Lancashire Evening Post: "I think it may well be out of our reach. I think they (West Brom) have intimated they would be prepared to sell him.
"But I think the fee they are looking for is pretty high. So high in fact that it may well be out of our reach."