Substitute Loughman had been on the field for only eight minutes when he was injured in the epic 33-31 win over Australia that opened Ireland’s campaign in Sydney at the weekend, and must undergo standard return-to-play protocols.
Baloucoune was forced to sit out that game with a hamstring injury and a decision on his involvement against Japan would be made later in the week, officials confirmed on Monday. Japan defeated Italy 27-10 in Tokyo in their first fixture.
Ireland coach Andy Farrell will name his side on Thursday.