Robbie Henshaw is an injury doubt for Ireland's World Cup opener against Scotland, the PA news agency understands.
The British and Irish Lions centre is thought to have suffered a hamstring strain in training in Chiba on Saturday.
The 26-year-old had looked all set to partner Bundee Aki in a robust midfield pairing for Ireland's Pool A opener in Yokohama on Sunday, September 22.
An injury threat for Henshaw now would leave Garry Ringrose likely to slot into the centres alongside Aki, though Chris Farrell could also provide a more direct replacement in the physicality stakes.
The versatile Will Addison was due to start Ulster's pre-season clash at Glasgow on Saturday, only to be shifted to the bench in the minutes before kick-off. He was then kept under wraps as an unused replacement as Ulster lost 36-33 in Glasgow.
Addison narrowly missed out on Ireland's 31-man World Cup squad but head coach Joe Schmidt highly values his abilities, especially in covering centre, wing and full-back – and fly-half at a stretch.
The former England Under-20s star would head the queue of replacements should Henshaw's injury concern be deemed serious enough to threaten his participation in the tournament.
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