Fin Smith has been spotted sitting out of England training as Steve Borthwick's side continue preparations for Sunday's clash against Australia.
England will take on the Wallabies at Allianz Stadium in their opening autumn fixture in the Nations Championship, before facing Japan and New Zealand.
They will also feature in the finals weekend, which will be held at the same venue.
However, England could be without their first-choice fly-half for the start of their campaign, with Smith spotted sitting out training at Pennyhill Park on Tuesday.
BBC reporter Chris Jones shared the update on his Instagram story, following Smith's absence from England's three-day training camp last week as a precaution. The Northampton Saints star was subsequently included in the final Nations Championship squad.
Smith also missed Saints' victory over Gloucester at the weekend due to the injury.
He is believed to be struggling with a calf problem, although England have yet to provide an official update on the severity of the issue or how long he could be sidelined.
Fellow Northampton half-back Alex Mitchell is another injury concern, with the scrum-half scheduled to undergo a scan this week on a hamstring problem.
Mitchell was left out of England's squad entirely after suffering the injury and managed just 21 minutes of Saints' win over Gloucester before being forced off.
Uncapped scrum-half McParland is also a doubt after picking up a calf injury during England training. The 20-year-old subsequently missed Northampton's victory over Gloucester.
Smith has established himself as England's first-choice number 10 in recent months, starting all three matches during the summer edition of the Nations Championship.
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At just 24, he is widely regarded as one of the country's leading fly-halves and has considerable potential to develop further. His standing was also highlighted by his selection for the British and Irish Lions' tour of Australia last year.
Should Smith miss Sunday's match, England are likely to turn to either Marcus Smith or George Ford, with both players looking to strengthen their positions in the national side.
Gloucester's Charlie Atkinson was brought into last week's training squad as cover for Fin Smith, making him another potential option should the Northampton fly-half be forced to withdraw.
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