• Scrum-half out of game against Australia on Sunday

• Wallabies match followed by New Zealand and Japan

The Northampton scrum-half Alex Mitchell has been ruled out of England’s November opener against Australia on Sunday, with Bristol’s Harry Randall and Bath’s Ben Spencer called into the squad named by the head coach, Steve Borthwick.

Mitchell, established as the first-choice No 9 under Borthwick, damaged a hamstring in Northampton’s Prem win against Gloucester on Saturday and will have a scan on Tuesday to determine the extent of the injury.

Archie McParland, Mitchell’s uncapped clubmate, is also sidelined for the Wallabies match after sustaining a calf injury training with England last week, following his second call-up to the senior squad. A major scrum-half rethink is consequently needed by Borthwick before a highly significant sequence of four Nations Championship matches.

The injury-enforced absence of Mitchell and McParland means either Randall or Spencer will be on the bench against Australia, with Leicester’s Jack van Poortvliet expected to start at No 9.

While Mitchell is guaranteed to return when he recovers from injury, this week represents a priceless chance for Randall and Spencer to state their respective cases, with the World Cup less than a year away.

Borthwick and his staff will consider how swapping Mitchell and McParland for Randall and Spencer may affect tactics against the Wallabies. Randall is famed for a sniping running game with Bristol while Spencer, who recently returned to action for Bath after shoulder surgery, is known for his exemplary tactical kicking.

Elsewhere in the back division Gloucester’s Seb Atkinson, Exeter’s Immanuel Feyi-Waboso and Fin Smith of Northampton are all named in England’s 36-man squad despite recent injury concerns. Max Ojomoh of Bath and Saracens’ Noah Caluori drop out of the group named eight days ago.

Meanwhile the in-form Harlequins fly-half, Marcus Smith, is widely expected to push his namesake Fin for the starting No 10 jersey while George Furbank, who is also in scintillating form for Harlequins, is a strong candidate to start at full-back.

There is one change to the forwards from the training squad named last week by Borthwick: the 21-year-old Bath hooker Kepu Tuipulotu, another uncapped player, drops out because of injury, with Theo Dan of Saracens returning.

Borthwick’s squad of 20 forwards and 16 backs gathered at Pennyhill Park on Monday night, with the Prem now on a break until December. After kicking off against Australia in round four of the Nations Championship, England will meet Japan and New Zealand in rounds five and six before the finals weekend at the end of November, with their last opponents to be confirmed.

“We’re looking forward to getting back to Allianz Stadium for four important Test matches against top-level opposition,” Borthwick said. “These fixtures take on added significance this autumn as they represent our final opportunity to face southern hemisphere opposition before next year’s World Cup.

“Facing Australia next Sunday is an exciting challenge. They have played a significant amount of Test rugby in recent months, and we know the quality and experience they will bring.”

Scotland have had a double injury blow of their own before the conclusion of their Nations Championship campaign, with Jamie Ritchie and Elliot Millar Mills ruled out of all four November matches.

Ritchie is expected to be out for four to six weeks after the flanker sustained a suspected medial collateral ligament injury in Glasgow’s United Rugby Championship win against Lions last Friday. The prop Millar Mills picked up a knee injury during Newcastle’s Prem defeat by Saracens on Saturday.

Three Edinburgh forwards – the props Ollie Blyth-Lafferty and D’Arcy Rae, and the flanker Freddy Douglas – have been called into Gregor Townsend’s squad. Scotland face New Zealand on Saturday before Tests against Australia and Japan, all at Murrayfield.