Makuhari - A hamstring injury will keep Robbie Henshaw out of Ireland's opening Rugby World Cup game against Scotland but the centre will stay with the squad after responding "reasonably positively" to treatment.
"Robbie's looking unlikely for this weekend," assistant coach Greg Feek told reporters on Monday following a scan on his injured hamstring.
"We just got back from training and we're still sorting things out but I think it's reasonably positive in terms of what we saw," added Feek.
"Some of these guys, day by day, week by week, things can improve dramatically (compared to) the average human."
The Leinster centre, 26, is suffering a painful case of deja vu as he also missed the first two games of the 2015 World Cup through injury but Feek refused to be drawn on when he might burst onto the scene in the tournament.
"It's still early days. We still have hopes for next week," he said.
Ireland start their World Cup campaign against Six Nations rivals Scotland in a Pool A that also contains hosts Japan, Samoa and Russia.
Henshaw will stay with the squad and is feeling "a sense of relief in many ways" that the injury was not as serious as feared, said the coach.
There was also positive news on other injury concerns, with winger Keith Earls and flyhalf Joey Carbery training well, according to Feek.
"Joey was running around today in training. He looked pretty good so happy for him more than anything," said the coach.
Ireland have three other centres to choose from - Henshaw's Leinster teammate Garry Ringrose, Bundee Aki and Chris Farrell - and flyhalf Jack Carty challenged them to step up into Henshaw's role.
"Robbie last week, you can see the energy he brought, especially in defence. Obviously, for himself it's probably a bit of a blow," said Carty.
"But if you look at the three lads who are there... when they're at their best, they're world class.
"It's obviously really bitterly disappointing for Robbie and he's working really hard to try to get back but I suppose it's an opportunity for the three other lads to step up," said the flyhalf.
Ireland come into the 2019 World Cup as the No 1 team after two warm-up wins against Wales put them narrowly ahead of the All Blacks in the World Rugby rankings.
But they are desperate to improve on a World Cup record that has seen them fail to progress beyond the quarter-finals.
They are hoping to send head coach Joe Schmidt out on a high after a remarkable six-year tenure that has included wins over all the southern hemisphere nations, a Grand Slam and three Six Nations titles.