Rob Kearney is understood to have become a new injury doubt for Ireland's World Cup opener against Scotland.
The experienced full-back is thought to have picked up a calf complaint in training on Monday, handing head coach Joe Schmidt an injury headache.
Robbie Henshaw is also "very, very unlikely" to be fit for Sunday's Pool A game in Yokohama due to a hamstring problem, according to scrum coach Greg Feek.
But losing Kearney would force Schmidt into another backline rethink, with Andrew Conway and Jordan Larmour in the frame to start at 15.
The 33-year-old Kearney impressed in Ireland's 19-10 victory over Wales that closed their World Cup warm-up fixtures in Dublin on September 7.
The 92-cap player ties Ireland's backline together and Schmidt will be keen not to lose such a calming presence.
Henshaw picked up a hamstring problem in Ireland training and is expected to miss the Scotland clash.
But Ireland have retained the 26-year-old in their 31-man squad and still retain hope he can recover in time to feature in the tournament.
Ireland have opted not to release the full extent of Henshaw's injury, but a team spokesman confirmed he will definitely not be returning home.
Asked if Henshaw had been ruled out of the Scotland match, Feek said: "Well not really but you can read between the lines. Robbie's looking very, very unlikely for this weekend obviously.
"But we've just got back from training and still sorting things out, but I think it's reasonably positive in terms of what we saw.
"Some of these guys, day by day, week by week, they can improve dramatically as opposed to the average human. So we'll just take it like that at the moment.
#RWC2019 @JoeyCarbery trained fully today. @KEITHEARLS87 is working away and is likely to train later in the week. #shouldertoshoulder pic.twitter.com/kmlWMTOnHG — Irish Rugby (@IrishRugby) September 16, 2019
"It's looking positive, so from here on in we'll just see how it goes in the next few days and then maybe reassess in the not too distant future."
Feek admitted Henshaw will be relieved by the positive news on his hamstring complaint, with Ireland still hoping he can shake off the issue quickly.
"He's a good man, great to have around, his work ethic is incredible and you know he's doing the work," said Feek.
"To be at this stage now there's probably a sense of relief."
Feek also confirmed that Joey Carbery trained fully on Monday, leaving him well placed to feature against Scotland.
Playmaker Carbery suffered an ankle ligament injury in Ireland's opening World Cup warm-up match against Italy in Dublin on August 10.
The 23-year-old had faced a race against time to be ready for Ireland's World Cup opener, but now seems to have pulled off that feat.
"Joey was running around today and trained, he looked pretty good," said Feek. "So we're just all really happy for him more than anything."
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