Morath has been replaced in the squad by Latiume Fosita after picking up a throat injury in the weekend's 35-3 loss to England.
He was hospitalised in Sapporo and is awaiting confirmation on whether he needs surgery or not.
Morath copped a stray boot when attempting to tackle England powerhouse midfielder Manu Tuilagi.
Nafi Tuitavake, who came on as a half-time replacement for wing Atieli Pakalani, broke his left arm late in the match.
A replacement has yet to be named for him.