Joe Root, the England captain, was admitted to hospital in Sydney, suffering from severe dehydration, amid doubts as to whether he would be fit to resume his rearguard in the fifth and final Test at the SCG.
In the end, Root did appear during the morning session, batting for an hour and taking his overnight 42 not on to 58 at lunch. However, he was again unable to continue after the interval and did not attend the post-match presentations after England were dismissed for 180 to lose by and innings.
"He's not had any sleep. He's not eaten. He's had diarrhoea and he's been vomiting, so I guess he's not in great state," James Anderson, England's vice-captain, said. "To get to the ground was a great effort, and to strap his pads on and bat for as long as he did was a brilliant effort and showed exactly what sort of character he is.
"He wants to lead by example in this team. He's been a fantastic captain on this tour and it shows what sort of person he is to make that sort of effort to get out on the field. I just hope it's not too serious and he can sleep it off now and get better before the one-dayers
Root, who batted for three hours on fourth day, had been in the field for all but six overs of the hottest day on record for a Test match in Australia. Temperatures in some parts of Sydney reached 47.3C, the highest in the city for 79 years.
Root succumbed to bouts of diarrhoea and vomiting overnight, and did not arrive at the ground until after the start of play. It was later announced by the ECB that Root was suffering from a viral gastroenteritis bug, rather than the effects of heat exhaustion.
Already 3-0 down in the series, England were precariously placed on 93 for 4 overnight, needing another 210 runs to make Australia bat again. Moeen Ali took the field alongside Jonny Bairstow at the start if play but Root was fit enough to resume his innings after Moeen's dismissal on the hour mark, and soon moved to his fifty.
Asked how Root had found the tour, Anderson said: "I imagine extremely difficult. Ask any captain who has toured Australia, it's not an easy place to come. Especially when on wrong end of results. The way he's carried himself has been a credit to himself. He's been fantastic the whole way through, as a guy he's not looked down at any stage. He's led the guys brilliantly both on and off the field. He should be very proud of what he's done on this trip."
Before it was made clear that Root was affected by a virus, there had been speculation about the damaging effects of playing in high temperatures. Dean Jones, the former Australia batsman who famously ended up on a drip after making 210 in oppressive heat during the tied Test in Madras in 1986, stated on Twitter that the sport needs to take the issue of exposure to extreme conditions more seriously.
"After speaking to a couple of doctors this morning.. in my opinion cricket should be called off after 41C," Jones wrote. "It's a workplace issue now.. just my opinion."