The Black Cats boss has backed the Republic of Ireland international to overcome the increased attention that defenders pay to him during games in order to improve his performances
The 23-year-old attacker arrived at the Stadium of Light in August 2011 from Airtricity Premier Division club Derry City and made his debut in O'Neill's first game in charge of Sunderland in December 2011, going on to score five goals in 23 league appearances in his first season.
Speaking ahead of Sunderland's Premier League clash with Tottenham Hotspur on Saturday December 29, O'Neill stated that it has been difficult for the former Derry City winger to adapt but stressed that he is beginning to improve.
"With James, we sat here a couple of months ago and we were talking about this second season syndrome, and I was hoping that it genuinely wouldn't be an insurmountable problem for him," O'Neill told reporters.
He added: "I knew he would have difficulty early on, and that was shown by the number of times that full-backs went to close him so very quickly in matches. He is learning to cope with that now and I am hoping he will overcome it.
"But still, he will have games where he will be unable to do anything, simply because players have either marked him or things didn't happen for him. But overall, he is coming through," concluded O'Neill.