Joe Schmidt is "scared" to spend too much time thinking about Ireland winning the Grand Slam ahead of Saturday's showdown with England.
Ireland already have the Six Nations title in the bag and a victory over the 2016 and 2017 champions at Twickenham would give them only a third clean sweep.
Schmidt is eager to avoid putting too much pressure on his side with so much at stake against an England side smarting from back-to-back defeats to Scotland and France.
The Ireland head coach said: "I don't know about the players, but I would be very much a glass half-full person. I get excited about the group we have and how hard we work, but I'd be very balanced from the perspective of being a pragmatist at the same time.
"There is no point in dreaming beyond this Saturday, because this Saturday is a finite point for us where a number of things have to happen and go right.
"I wouldn't say that you can control of that emotional rollercoaster that preparing a high-level sports team kind of engenders, because there are times where you inevitably imagine the worst-case scenario.
"Worst-case scenario is that England hit the ground running and they actually win with a bit to spare. That would be a bit of a crushing scenario. It would be a crushing way for us to finish a year of being unbeaten.
"A potential opportunity that has only been done twice before, I'd be more motivated and scared by that than thinking about how fantastic it would be to do something that would be another step for this group into kind of stretching themselves beyond what they’ve done before."
