Campbell has endured a torrid 18 months with injury problems but has returned to first-team action in fine form with a couple of goals to remind the Sunderland fans of his talent.
O’Neill has been boosted by the return of the 24-year-old but with the England squad dominated by high profile stars, the inclusion of Campbell was one that few saw coming.
"There are some terrific players there and getting a place in the squad is extremely difficult," O’Neill told the clubs official website. "He has only had a couple of games back.
"It's a boost, even just to be in involved for a few days. It's fantastic. Whether he does or doesn't play, to me, is immaterial at this stage.
"The news is a great boost... I think it would have been a bit of a surprise for him.
"If he gets the opportunity it would be great to take it."
Campbell has scored just 6 goals in 45 Premier League appearances since making the breakthrough at Manchester United in 2007.