O'Neill's charges are guaranteed second place in Group C behind Germany regardless of the result of their final qualifier against Norway in Oslo on Sunday.
However, only eight of the nine second-placed teams in the groups advance to the playoffs, and Northern Ireland must wait on other results before their place in the next round is confirmed.
The Green and White Army will advance to the playoffs if Greece fail to beat Cyprus on Saturday, night but O'Neill will only focus on his own team and not leave qualification to chance.
"We're not going to approach the game like that," O'Neill told Sky Sports News. "I think when we beat the Czech Republic so many people misinterpreted that in the media and said that we had guaranteed a playoff place.
"We never thought that for one second. We obviously were delighted to guarantee ourselves second in the group but you can see the way the groups are finishing - so many teams still have so much to play for. We're in a strong position but equally we have to come here and make sure we take something from tomorrow night to make sure we guarantee ourselves the opportunity of a playoff place.
"We have to approach the game with the mindset of getting a result, make sure we're difficult to beat and obviously try to win the game as well. There are too many variables. We have to get the players in the right frame of mind, which they are. They know the job at hand and what's required of them tomorrow night."
Northern Ireland need a point from the game against Norway to ensure a World Cup playoff spot.