Australia spinner Nathan Lyon suffered a “significant calf strain” on day two of the second Ashes Test and is a doubt for the rest of the series.
Lyon pulled up when running to field a ball and had to be helped by the physio as he walked back to the dressing room.
The 35-year-old has not returned to the field since and arrived at the ground on crutches before day three.
Cricket Australia said he will “require a period of rehabilitation after this match is concluded”.
“A decision regarding his availability for the remainder of the series will be made at the conclusion of the game,” they added.
Lyon could bat, if required, later in the game.
Earlier in England’s innings, Lyon took his 496th Test wicket by dismissing opener Zak Crawley.
The off-spinner took eight wickets in Australia’s victory in the first Test at Edgbaston last week.
“We’re going to miss him for this game and could miss him for quite a while,” said Australia batter Steve Smith after day two.
“It didn’t look good. It would be a big loss for us.”
Lyon is playing his 100th consecutive Test, only the seventh player in history and first bowler to do so.
After Lyon left the field, Australia took three England wickets for 34 runs to leave the home side 278-4 at the close, 138 runs behind.
England captain Ben Stokes was dismissed by Mitchell Starc in the first over of day three.
Off-spinner Todd Murphy, who made his debut in February and has played four Tests, is the only other spinner in Australia’s squad.
Murphy, 22, returned figures of 7-124 in his first Test against India and took another seven in the rest of the series.