England have lost Alex Mitchell for the entire autumn because of the hamstring injury sustained on Northampton duty over the weekend.
Mitchell on Monday underwent a scan on the damage incurred in the 28-14 Gallagher Prem victory over Gloucester, with the results confirming the British and Irish Lions scrum-half will miss all four of this month's Tests.
It is the fourth hamstring injury Mitchell has suffered in 2026 in another blow to a player who was set to play a full role against Australia, Japan and New Zealand, as well as in the Nations Championship's finals weekend on Nov. 27-29.
Jack van Poortvliet is likely to continue in the No. 9 jersey in his absence, with either Ben Spencer or Harry Randall providing cover from the bench.
Mitchell's Northampton team-mate Fin Smith is facing a race against time to be fit for the Wallabies' visit to Allianz Stadium on Sunday as he battles his second calf problem of the year.
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Head coach Steve Borthwick will give Smith until Wednesday to prove he can take part in the match, with George Ford and Marcus Smith on standby to replace him at fly-half.
Archie McParland, another Northampton half-back who is struggling with a calf issue, could return against Japan or New Zealand, but Sam Underhill (biceps), Kepueli Tuipulotu (knee) and Benhard Janse van Rensburg (concussion) will miss the whole of the second phase of the Nations Championship.