The teams meet at the Aviva Stadium with the Irish two points behind third-placed Scotland, who won 1-0 – courtesy of a Shaun Maloney goal – when they met at Celtic Park last November.
Victory in the reverse fixture would keep the home side firmly in the hunt for one of the two automatic qualification places in Group D – currently occupied by Poland and Germany – but defeat would realistically end their chances of making it to the finals in France next summer.
“It’s a great match to be involved in,” said O’Neill. “Eventually you come to a stage where you start out in the group and you come to crunch matches, and this is very important.
“We don’t want Scotland to get too far ahead of ourselves and give ourselves a mountain to climb for the last four matches.
“It would be important to win the game, and we’ll be right there. If we lose the game, the gap with only four matches left, becomes difficult but there will be a few twists and turns until you complete the group.
“We have some home matches and we want to take advantage of that.”
O’Neill gave little away in terms of team selection for the Scotland game, where his main dilemma is likely to be whether to play Robbie Brady or Stephen Ward at left-back.
“I have an idea of the team, but there is plenty of time between now and Saturday. There is plenty of time before Scotland,” he added.
“I’ve been doing this job, management, for quite some time. I’m okay. I’m happy enough with it myself. Be relaxed.”
Meanwhile, O’Neill confirmed he is fine following a car crash in Dublin on Tuesday night in which a vehicle being driven by his assistant Roy Keane was hit from behind on a motorway.