The highly rated midfielder received his first England call-up at the weekend.
O’Neill said: “James knows what he has to do now. He has got the ability.
“He feels he has got much more to give and much more to learn.
“He has still to realise his potential — he knows that himself.
“But he is making very good progress at the moment.
“The most important thing for him now is to play consistently well enough in the next year-and-a-half and keep going.
“If he does, I think him getting on that plane to South Africa would be a certainty.
“I think that’s a goal in itself because England will be there and it would be a great reward for him.”