Alex Mitchell and Archie McParland have been ruled out of Sunday’s autumn opener against Australia in an escalation of the disruption faced by England at half-back.

With first-choice fly-half Fin Smith engaged in a race against time to recover from a calf strain in time for the Wallabies’ visit to Allianz Stadium, England have been forced to rule scrum-halves Mitchell and McParland out of contention.

Mitchell damaged his hamstring when on Northampton duty against Gloucester on Saturday and is to undergo a scan, placing his involvement in the second phase of the Nations Championship in doubt.

McParland missed the 28-14 victory at Franklin’s Gardens because of a calf issue sustained during England’s training camp last week and it is hoped he will recover in time to face Japan or New Zealand later in the month.

To fill the vacancies created in his 36-man squad, head coach Steve Borthwick has called up Ben Spencer and Harry Randall.