Joe Schmidt is not yet ruling Rob Kearney out of Ireland's World Cup opener against Scotland on Sunday.
Kearney does have tightness in his calf, according to a team spokesman, but could even resume running when the squad train again tomorrow.
But if he doesn't, Kearney would have to wait until Ireland's next training session on Friday to prove his fitness and that would make him a major doubt for the Yokohama clash.
"There was a bit of a flurry last night about Rob Kearney," said Ireland press officer David O'Suiochain.
"He's got a bit of tightness in his calf.
"That's going to be managed today. There's no training today, it's a down day and it's hoped that he will be out running on Wednesday, so we'll be able to update again on Wednesday how he's going.
"The plan is hopefully that he'll do a bit of running, that it will ease up and if not Wednesday, he'll have a run on Friday.
"Today and Thursday are down days, we train Wednesday, we train Friday at Yokohama Stadium and then Saturday we can't get into the stadium with the game on (New Zealand v South Africa) so there's no official captain's run."
O'Suiochan added that centre Robbie Henshaw was "not likely" to feature against the Scots due to his hamstring issue.
"Hopeful that beyond that he'll be back up and running, running into Japan week," he added.
Keith Earls, who has recovered from tendonitis in his knee, was able to run during Monday's training session while Joey Carbery trained fully having recovered from his calf injury.
