"Maybe in a week or two, we might have to look at prioritising," O'Neill told the club's official website.
"Had we been halfway up the Barclays Premier League in this particular season and safe from relegation, then, of course, the cup competitions would have become very important.
"But we are battling [in the league] at the moment.
"We will treat this FA Cup in the right manner - as a real proper cup tie - and try to get through.
"But there might be a point in prioritising. I don't know. A lot will depend on what happens in the transfer market in the next fortnight."