Tommy Freeman, Mitchell’s team-mate for club and country, said it was “gutting” news for his colleague but backed him to come back stronger.

“It will definitely give him time to go after his rehab and get to the bottom of what is going on, find new solutions and ways to maximise his recovery,” Saints wing Freeman said.

“You don’t want to see your mate and a player who is a massive part of this group out. He is going to be missed with his humour off the field and playing ability on it.”

Freeman said Smith is “pretty optimistic” about playing against the Wallabies and despite a reduced role in training is making up for it in other areas.

“He’s joining in with meetings and giving good points so he’s very much involved and that shows the character he is,” he added.

Bath’s Ben Spencer and Bristol Bears’ Harry Randall were called in as scrum-half options on Monday, with Leicester’s Jack van Poortvliet – who started all three of England’s summer Tests – the likely first-choice nine.

Northampton scrum-half Archie McParland, 21, was named in the initial training squad but has withdrawn with a calf injury.

Hooker Luke Cowan-Dickie and flanker Tom Curry both took part in modified training on Tuesday at England’s Bagshot base, but are expected to be fit for selection.

England boss Steve Borthwick will name his side to face Australia on Friday.