The Saracens lock started Saturday’s crucial 25-17 win over the Wallabies in Brisbane, but was withdrawn shortly before half-time after suffering a heavy blow to the head during an attempted tackle on Australia centre Hunter Paisami.
Itoje received swift treatment with the game quickly stopped and was able to walk off the field for a head injury assessment (HIA), replaced by Leicester’s Ollie Chessum.
The influential 27-year-old did not re-emerge for the second half at Suncorp Stadium and has already been ruled out of next week’s mammoth winner-takes-all final showdown at the SCG.
“The medical situation with Maro is that he will be out next weekend,” England head coach Eddie Jones confirmed to reporters in his post-match press conference.
Australia’s woeful luck with injuries also continued in the second Test, with Jordan Petaia - starting at full-back with Tom Banks and Andrew Kellaway both sidelined - suffering his own head injury within minutes of kick-off.
He’s been ruled out of the third Test along with Itoje, as has his replacement Izaia Perese, who was carted off early in the second half with a serious-looking non-contact knee injury that left him in agony.
Australia will also be without lock Cadeyrn Neville and prop Scott Sio at the SCG after the duo were also injured in the second half on Saturday.
England’s Sam Underhill also went off after a head knock and will be monitored in the coming days. The Bath flanker came into the team in Brisbane as a replacement for Tom Curry, who has flown home for further assessment and management after suffering another concussion in Perth.