Joey Carbery did not travel to Tokyo with the Ireland squad after a scan over the weekend revealed an ankle strain. This was largely expected after Carbery's pulled up 50 minutes into the 55-19 victory over the USA.
Paddy Jackson, who was named in the initial squad but did not travel to New Jersey, has linked up with the team and is expected to start against Japan this Saturday at the Ecopa stadium in Fukuroi.
"Joey is not here," confirmed Ireland assistant coach Richie Murphy. "The ankle will need four to six weeks to recover. Tiernan O'Halloran had cramp but should be okay."
Carbery’s injury is not believed to be related to the syndesmosis that required surgery last December.
There has been no contact, meanwhile, from the British and Irish Lions despite Scotland fullback Stuart Hogg being ruled out of the New Zealand tour.
Lions coach Warren Gatland does have the benefit of Wales being based in Auckland ahead of their test match against Tonga.
