The Black Cats are believed to have had two bids turned down for the 25-year-old already this summer.
However, Wolves have since loosened their stance over the centre-forward, according to Sky Sports News.
It is believed that the Championship side had originally demanded £15m for the former Scottish international. Now, the asking price is said to have dropped to around £10m.
Fletcher missed Saturday's 1-0 loss to Leeds United.