Peter Handscomb fell ill in stifling heat as Australia reached 2-225 at stumps, trailing Bangladesh by 80 runs, on day two of the second Test in Chittagong.
Handscomb received medical treatment but played through Tuesday’s last session to finish on 69 not out as the visitors took control of the match after dismissing Bangladesh for 305.
David Warner was unbeaten on 88, delivering another big subcontinent score after making a century in the first Test in Dhaka.
Lyon is again Australia’s best with the ball
Nathan Lyon earlier took his tally for the innings to seven wickets to continue his excellent series.
Play was paused for about five minutes late in the final session when Handscomb pulled up on his haunches, looking clearly unwell after running between the wickets.
The 26-year-old sat on the ground and was examined by team doctor Geoff Verrall, who applied cold towels to his head and neck.
The Australians have struggled with the conditions throughout the match, with sole quick Pat Cummins receiving treatment on Monday for a heat-related illness.
Handscomb, who showed sublime footwork during his stylish knock, faced 113 deliveries in the difficult conditions, while Warner dealt with 170.
After scoring an aggressive ton in Dhaka, Warner changed gears with a patient and composed knock to bring up his 25th Test half-century from 98 balls.
The left-hander was dropped on 52, with Mominul Haque putting down a difficult chance at short-leg off the bowling of Taijul Islam.
He also benefited from a bungled stumping on 73, with Bangladesh skipper Mushfiqur Rahim fumbling the ball when Warner danced down the pitch and missed an attempted slog.
Mushfiqur, who top-scored for Bangladesh with 68, had earlier taken a spectacular diving catch off the bowling of paceman Mustafizur Rahman to dismiss Matt Renshaw (4).
It was an excellent afternoon session for the Australians, who had looked somewhat vulnerable when skipper Steve Smith threw his wicket away shortly before tea.
Smith’s good form undone by one bad moment
The Australian skipper was on 58 when he was clean-bowled by a straight delivery from left-arm spinner Taijul shortly before tea.
Smith fumed as he walked from the ground after leaving an inviting gap between bat and pad for Taijul to exploit in his first ball of the innings.
He had looked in imperious touch, reaching his half-century from 81 balls and twice dispatching dangerous left-arm spinner Shakib Al Hasan for four with audacious standing sweep shots.
Lyon earlier finished with 7-94 – his fourth seven-wicket haul and the equal-second best figures of his career after claiming 8-50 against India earlier this year in Bangalore.