The tourists expect Root will resume his innings, if required, at some point on Monday after he was discharged from hospital.
Root finished with an unbeaten 42 at stumps on day four of the series finale, having spent most of Sunday in the field being baked in record-breaking heat.
England resumed at 4-93 on day five, trailing Australia by 210 runs.
An England team spokesman confirmed Root's hospitalisation, noting he was severely dehydrated with diarrhoea and vomiting.
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Root spent the most time in the middle of all players in Sydney's Sunday heatwave, fielding for the first half of the day before being called to the crease just six overs into England's innings.
Temperatures at nearby Bureau of Meteorology stations reached 43.4 and 43.7 degrees, above the record 43.1 taken during the 1908 Adelaide Ashes Test.
A heat stress tracker, which takes into account environmental factors for a 'feels like' mark, at the ground also displayed a reading of 57.6C in the middle.
Root's absence has exposed England's lower order and tail, with the out-of-form Moeen Ali summoned to the middle after his skipper retired hurt.
The dehydration has added further insult to a right index finger injury sustained by Root on Sunday night, after he attempted to pull a Mitchell Starc ball in the final session.
At the time he brushed it off as minor, and England coaching staff were confident he would be able to bat through it on Monday morning.
"I think it's just sore," assistant coach Paul Farbrace said after play.
"Before I came out I said 'How is it'? And he said 'sore' and he said 'It'll probably be a bit stiff in the morning'.
"I think regardless of how it is in the morning, he'll be taking guard first ball, that's for certain."
