Gray has pleaded the Wearsiders to act fast before the season kicks off next weekend.
"He's a very good player, he's a goalscorer and that's what Sunderland have been missing," Gray told the Sunday Sun.
"I don't think they have ever replaced Darren Bent.
"But Steven Fletcher scored 12 goals in what you would have to say was a poor Wolves side last season, so he'd be playing with better players around him.
"And he would get great service from Seb Larsson and James McClean out wide."