Melbourne - Joe Root is set to play for England in Sunday's opening one-day international in Melbourne after recovering from a viral illness, but Australia opener David Warner is troubled by a stomach bug.
Root was hospitalised on the final morning of the fifth Ashes Test in Sydney with gastroenteritis but England ODI skipper Eoin Morgan said he would play in the series opener in Melbourne.
"Joe is good and should be fit to play tomorrow," Morgan told reporters on Saturday.
"He's extremely important. He's been a fantastic leader within the group and, on top of that, there's the weight of runs he's scored and the manner that he's scored them.
"He's obviously a key part. He's a very versatile player and can score in any strike-rate that needs to be required, given the situation."
But while Root was in better health, Australia vice-captain Warner missed the team's final training session on Saturday and instead walked laps of the Melbourne Cricket Ground.
"I think he's okay, he was having a bit of a gastro issue yesterday," skipper Steve Smith told reporters.
"He turned up here today and walked the oval a few times. He said he'll be fine so I don't think there'll be any trouble there."
Warner, the No 3-ranked ODI batsman, has been one of the game's most dominant 50-over players, especially playing at home.
Since Australia's World Cup final win at the MCG in 2015, the left-hander has averaged more than 80 from 11 games in Australia, including five centuries.
Warner has scored 156, 144, 16, 103 and 86 in his past five innings at the ground in all formats.
He is the latest player to be struck down by illness in recent weeks, joining team-mates Steve Smith and Patrick Cummins as well as Root, who have all been affected by stomach problems since Christmas.
England were thrashed 4-0 in the five-Test Ashes series by Australia but have had better results in the 50-over format.
They have a better record than any other team since the last World Cup winning 34 of 53 matches.
England are the only team since the World Cup with a strike rate above a run a ball (6.3 per over), have scored the most totals in excess of 300 (24) and two of more than 400 while their batsmen have hit more fours and sixes than any other team.
Steve Smith (captain), David Warner, Pat Cummins, Aaron Finch, Josh Hazlewood, Travis Head, Mitchell Marsh, Tim Paine, Jhye Richardson, Mitchell Starc, Marcus Stoinis, Andrew Tye, Cameron White, Adam Zampa
Eoin Morgan (captain), Moeen Ali, Jonny Bairstow, Jake Ball, Sam Billings, Jos Buttler, Tom Curran, Alex Hales, Dawid Malan, Liam Plunkett, Adil Rashid, Joe Root, Jason Roy, David Willey, Chris Woakes, Mark Wood