The Black Cats find themselves sitting 16th on the table after 14 league outings and O'Neill is desperate to improve that by adding to his squad in January.
"We will try to strengthen if we can do," he said.
"Most people will tell you that maybe it is not the best time but I have done it in the past and the players I have taken in in the January transfer window have proved pretty successful, the likes of Ashley Young (from Watford to Aston Villa in 2007).
"It is the one opportunity during the course of the season that you get, and it would be inappropriate for us not to have a look at that.
"If you were thinking about somebody that you feel is capable of doing something pretty OK for the club for the next couple of years, then January is no different to the summertime."