Jack Carty has the ideal chance to prove Ireland can hit top level without Johnny Sexton in Saturday's clash with Japan, according to Greg Feek.

Connacht fly-half Carty will make just his second Test start when Ireland take on World Cup hosts Japan in Shizuoka this weekend.

Ireland are adopting an ultra-cautious approach to Sexton's recovery from a bang to the thigh suffered in Sunday's 27-3 victory over Scotland in Yokohama.

Head coach Joe Schmidt has opted to omit the British and Irish Lions star entirely from Saturday's squad to face Japan, with Carty starting and Joey Carbery on the bench.

Scrum coach Feek believes Carty has raced forward in his progress in his first year of Test rugby, having made his debut in February – and backed the 27-year-old to prove his elite class this weekend.

Asked if it is a facile view that Ireland cannot function without Sexton, Feek said: "Yes 100 per cent; Jack Carty's been involved in all our games this year.

"For that alone is huge, there's huge amounts of growth, particularly when Johnny Sexton was World Player of the Year and there's almost a bit of osmosis being around him. You've got to get as much knowledge out of him as you can.

"You've got people around that can make him (Carty) such a better player.

"Then obviously with Joe (Schmidt), his analysis on our own players is at a point where Jack wouldn't have been in our squad all year, whether it's on the bench or starting, if he didn't have the right tools to what we want need to do, and to understand the game and understand what fits our group and how best we may be able to play.

"I think that shows for me the character of Jack really, ultimately it's about him being able to come in and be overawed probably initially for the first few weeks; even just walking next to Peter O'Mahony for him would have been pretty surreal.

"And then to soak up all the detail and be able to action that, and now it's really just up to him.

"So I just need to give him a big pat on the back for that."

Former All Blacks prop Feek has been combining his role as Ireland's scrum coach with a stint at Japan club side Ricoh, and insisted Schmidt's men expect a stern test against the tournament hosts this weekend.

"Over the last couple of seasons there's been a real emphasis of Japan getting their scrum up to an international standard, and you can really see that," said Feek.

"My knowledge of Japanese scrummaging goes back about 15 years. There's a real culture around the scrum.

"A lot of the company teams will travel two hours to have a live scrummaging session against each other. There's a thirst for knowledge to get better.

"We're under no illusions that this week will be tough, knowing the proud nature of Japanese rugby."