Danny Rose is back in training - and came through a midweek practice match unscathed.
The defender, who has missed the last two games with a hamstring problem, had returned to parent club Spurs for treatment.
But he's now back on Wearside and featured in a friendly clash with the development squad at the Academy of Light.
Boss O'Neill felt the outing was a worthwhile exercise and is pleased to have the England U21 international back in the fold.
"Danny had trained down at Tottenham, who wanted to keep him down there until he was properly fit and ready to join in on a regular basis," he said.
"We had a little game behind closed doors where a lot of the players I felt needed some football played against some of the younger lads.
"That gave me an opportunity to study both [sets of players].
"Danny played in the game, which should help him psychologically knowing he's played some part of a competitive game - and he feels not too bad about it."