Itoje required on-field treatment during the first half after colliding with Hunter Paisami shortly before half-time. The England lock then left the field for a head injury treatment and did not return for the second half.
Underhill was replaced during the second half of the 25-17 victory at Suncorp Stadium having suffered a head injury while tackling wing Marika Koroibete and he has now been stood down for Saturday’s clash.
No replacements will be called up, with Lewis Ludlam and Ollie Chessum likely to start in the pair’s place at the Sydney Cricket Ground for the decider.
It comes in the wake of Tom Curry returning home last week after being concussed in the first Test and England have only escaped a full-blown injury crisis at flanker by the news that Jack Willis has been cleared to train.
Additional reporting by Press Association.
