Republic of Ireland take on Denmark in Aarhus as they attempt to win their first game in the Nations League, having seen Ireland's rugby team dominate New Zealand on Sunday.
Martin O'Neill said: "The rugby team are brilliant, it's the strongest Irish side that I have ever known since I was growing up.
"No longer these days do you play international rugby and fade with 20 minutes to go, the lads are very, very strong.
"It's a totally different sport, of course. Yesterday was fantastic, absolutely fantastic to win, to beat the All Blacks. It's a major confidence boost for the World Cup coming up.
"But it's not that long ago since we were playing and enjoying ourselves [at the Euro 2016 finals] in France and trying to get to the play-offs in the World Cup."
"Since the World Cup match, we have played eight games, five of them friendly matches. If we were looking at decent stats and things, we wouldn't have chosen in recent times Turkey, Poland away, France - who went on to win the World Cup - away from home.
"We could confine ourselves to playing sides that might measure up to us, so those sort of things have never bothered me."