The 26-year-old former Leeds forward is available on a free transfer after a injury-hit spell with the Black Cats.
Robins chairman Steve Lansdown said: "We have opened talks with Sunderland and are hopeful Michael will be joining us.
"We would obviously want him to undergo a stringent medical. But he's a quality player. If everything is okay with the fitness, he could be a big signing."
Robins chairman Steve Lansdown said: "We have opened talks with Sunderland and are hopeful Michael will be joining us.
"We would obviously want him to undergo a stringent medical. But he's a quality player. If everything is okay with the fitness, he could be a big signing."