The 21 year-old was signed by Steve Bruce in the summer of 2011 but has yet to feature for the Black Cats this season despite his cult-like status amongst Sunderland fans for his match-winning goal against Manchester City on the first day of 2012.
Recent reports suggested that the South Korea international could be permanently on his way back home to Chunnam Dragons, but O'Neill is leaning towards a loan spell for the talented forward.
"He has found it difficult to cope with the physical aspect but he has natural talent and it is really up to him," said O'Neill.
"There have been a number of inquiries about our players and all I can say is that it has been a frustrating time for him.
"He played in the Olympics, didn't always start the games but he perhaps thought after that goal it would be lift-off time.
"If there was a possibility of a loan spell, I would give it some consideration, although I can't at the minute while we consider in-coming players."