Joe Schmidt's "incredible impact" has made Ireland believe they can beat anyone in the world, according to Rhys Ruddock.
Flanker Ruddock will captain Ireland in Saturday's Dublin Test clash with the United States, with boss Schmidt having made 14 changes from the side that stunned back-to-back world champions New Zealand 16-9 last weekend.
Head coach Schmidt will announce his decision on his long-term future next week, with the Kiwi expected to return to his native New Zealand after next year's World Cup when his Ireland contract expires.
Schmidt has guided Ireland from eighth to second in the world rankings and overseen three Six Nations titles in five years - and Ruddock believes because of the 53-year-old the men in green now fear no one.
"I think probably from an outsider's point of view, what you see, it's pretty black and white. Joe's impact, it's there for everyone to see," said Ruddock.
"It's obvious he's an incredible coach and he's had an incredible impact on the environment as well in Leinster. I was able to experience that first-hand and now with Ireland as well.
"But the impact he has on the group, and the belief over the long term, that has grown and grown. We're very lucky we've got him and the other coaches in the set-up doing such a great job.
"When I was younger I wasn't always able to see quite what he was trying to teach, but as you progress you see those intricacies. His rugby knowledge is second-to-none.
"Up until now we've done well and done what we can, and the work done behind the scenes and producing big performances and results, that just feeds the belief all the time.
"But the most important thing now will be the next few months leading into the World Cup.
"We want to go into the World Cup in good form, but right now for the group is a big challenge this weekend."
