Swindon midfielder Louis Thompson has agreed a move to Norwich, while Southampton's Jack Stephens has joined Town on loan.
The 21-year-old South Korea international has become an increasingly peripheral figure at the Stadium of Light, although he was included among the substitutes for Saturday's 2-1 Premier League defeat by Tottenham.
However, amid speculation that former club Chunnam Dragons may be keen to take him back, O'Neill has revealed he will look at the options next month, but only after he has completed his efforts to strengthen his existing squad during the winter transfer window.
Ji announced himself in style on Wearside on New Year's Day last year when he came off the bench to score the goal which condemned Manchester City to a 1-0 defeat.
The manager said: "There have been a number of enquiries about not only Ji, but a number of our players, and I am unable to tell you anything at this minute.
"All I can say just from the general viewpoint is it's been a frustrating time for him just recently.
"He played in the Olympics, he didn't always start the games, I know, for South Korea, but perhaps after that goal against Manchester City a year ago, maybe he was hoping it would be lift-off time for him.
"He's found it difficult, he's found it difficult to cope with the physical aspect of the game.
"But he has natural talent and it's really up to him. But if there was a possibility of a loan spell perhaps, I will give it some consideration.
"I can't really consider that at this minute until we look to see what we might be able to do with incoming players."
O'Neill has relied heavily on summer signing Steven Fletcher so far this season with Stephane Sessegnon playing off him and Louis Saha and Connor Wickham providing the back-up.
Fraizer Campbell has also been used as a substitute in recent games, but the fact that the Black Cats are in talks with New York Red Bulls over a loan move for former Everton start Tim Cahill suggests he is looking for fresh firepower.