Joe Schmidt has admitted Robbie Henshaw is "likely" to miss Ireland's World Cup opener against Scotland.
Head coach Schmidt admitted Henshaw pulled up with a tight hamstring in training on Saturday, leaving the Leinster star struggling to be ready to take on the Scots in Yokohama on Sunday.
The Ireland boss confirmed however that Ulster's Will Addison has not been called out to Japan as yet, with the Kiwi coach hoping that Henshaw can still play a part in the tournament.
British and Irish Lions star Henshaw's absence would prove a sizeable loss to Ireland for their crucial Pool A opener, but Schmidt is confident in the depth offered by Bundee Aki, Garry Ringrose and Chris Farrell as alternative options at centre.
"Robbie pulled up with a tightness in his hamstring, he has a scan at 2pm today (Sunday) and that will give us more information," said Schmidt.
"I just have to wait for more news.
"I think the fact that he pulled up, he wasn't accelerating at the time, we'd be hopeful it's not too bad.
"Is it likely to rule him out of this week? Yeah you'd have to say it is likely, the fact that he did pull up.
"But we'd be hopeful it's not too bad. I don't want to guess when we'll get the scan this afternoon."
Ulster dropped Addison to the bench for their pre-season clash in Glasgow at the weekend, but Schmidt insisted the former England Under-20s star has not been called out to Japan.
Asked if Addison had been called up as cover, Schmidt said: "No he's not on his way over.
"That was precautionary, just to make sure that we had fit and able cover should we need a replacement for Robbie.
"We'll have to wait for the results of the scan to find out exactly Robbie's issue, but it could yet just be a cramp or something like that, because we've been travelling of course.
"But if it is more than that and we do leave him out this week, we do feel we've got good cover in the centres."