The 60-year-old has endured a tough few weeks with Sunday's 2-1 defeat at former club Norwich extending the Black Cats' recent barren run to just two league victories in 22 attempts. That has left them perched nervously only a point and a single place above the relegation zone.
However, buoyed by a vastly-improved second half display at Carrow Road, O'Neill said: "We have got a really big month ahead and a lot of games - as has every side in the Premier League - so it is tough. But it doesn't mean that you shouldn't be thinking of looking at the January market as everybody does."
He continued: "All the clubs in the Premier League will be looking at it. If people are very active or inactive, I just don't know, but we will certainly have a look at it."
Sunderland entertain Chelsea on Saturday desperate for a first home win since they beat Wigan on Wearside on September 29, and knowing new Blues boss Rafael Benitez needs a victory just as much as they do, if for very different reasons.
Both O'Neill and owner and chairman Ellis Short had hoped their significant investment had been done during the summer when they splashed out a total of £22million on Scotland striker Steven Fletcher and England winger Adam Johnson, men who have endured differing fortunes at the Stadium of Light to date.
But with skipper Lee Cattermole facing a lengthy spell on the sidelines with a knee injury and both key defender John O'Shea and Fletcher currently on the injured list, the manager's resources are being stretched.
Just what that will mean in the longer term is unclear as yet, but O'Neill hinted last weekend that he could be in the market for reinforcements next month, and sources on Wearside have suggested Short could be ready to back him once again, although to what extent remains to be seen.