Ben Stokes left the field during the second day of the fourth Ashes Test with "left side tightness".
Another difficult session for the tourists, who have already lost the series after Australia won the first three matches, saw the hosts move to 209-3 as Steve Smith and Usman Khawaja built a partnership of 92.
Khawaja was dropped by Joe Root as England went wicket-less in the first session at the Sydney Cricket Ground, but a more worrying sight came when Stokes went off clutching his side after sending down a series of short balls.
And England subsequently released an update during lunch that confirmed he was being treated for left side tightness and "would be assessed over the next hour".
Stokes, who returned to the side for the series after taking a break to protect his mental well-being, has scored 101 runs with the bat at an average of 16.83. With the ball, the all-rounder has taken four wickets.