Fit-again Amanaki Mafi could step into Japan’s starting back-row for the Pool A encounter in Shizuoka, with Leitch set to take a seat on the bench.
South Africa-born flanker Lappies Labuschagne could captain the Brave Blossoms in Leitch’s absence.
Number eight Kazuki Himeno admitted Japan were “spun” by the size of the occasion in the tournament opener, as they struggled to cope with the weight of host-nation expectation.
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“It wasn’t like a usual Test match there was a different atmosphere, the crowd noise was really loud and a few things spun us during the game,” said the 25-year-old Sunwolves back-rower.
“But it’s important we get back to our basics, what we are good at.
“We need to find out what’s going wrong and fix it on the spot. So as a leader that would be my focus; don’t get narrow or any tunnel vision because we need our peripheral vision and a sense of the game so we can fix problems on the spot.”
Wing Lomano Lemeki was bold enough to give a score prediction for the Ireland battle, insisting Japan will triumph.
The 30-year-old flyer was happy to accept that Japan failed to cope under the high ball against Russia, as those nerves bit hard.
The Brave Blossoms have been at pains to relax this week and stay calm ahead of a match that will go a long way to determining the outcome of Pool A.
Ireland will move towards topping the pool and a likely quarter-final with South Africa with victory, while Japan could heap huge pressure on both the Irish and the Scots should they instead prevail.
Asked who will win in Shizuoka, Lemeki replied: “I think we’ll win 33-26. Why? Because we train hard, and (Johnny) Sexton is not 100 per cent.”
When quizzed on how to cope with fielding high balls, Lemeki said: “Just catch the ball! Catch the high ball first of all, and if we catch it we can attack.
“I just need to do my best. As long as we can catch the ball it will be no problem.”
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