The 31-year old centre-half has fallen down the pecking order at the Stadium of Light in recent times, mainly due to injury problems.
O'Neill is convinced that Bramble, who arrived from Wigan Athletic in 2010, can force his way back in to the Black Cats first team provided he remains injury-free.
"Titus's problems are always about staying fit. It is always a balancing act with Titus in training during the week - we have to get as much training into him without aggravating any injuries, or risking swelling of the knees," he told the Shields Gazette.
"It's a shame because you can see just how good he could have been had it not been for the injuries, but he still has a lot to offer.
"He's bigger and stronger than he looks too. He won't get out-muscled by anyone."