UPDATE: England skipper Joe Root was ultimately forced to retire hurt as his horror Ashes campaign ended with him asleep in the rooms when Australia completed their 4-0 series win.

Root had been set to resume his innings on the fifth morning of the fifth Test at the SCG, but he arrived at the ground late due to a viral bug that left him hospitalised with severe dehydration, vomiting and diarrhea.

The skipper eventually did walk out to bat at the fall of the first wicket on Monday and bravely pushed on to his fifth half-century of the series to be 58no at lunch.

Root posts defiant fifty as England fight at the SCG

But he didn't return after the break and vice-captain Jimmy Anderson, who spoke at the post-match presentation in Root's absence, said the skipper was so unwell he'd fallen asleep in the rooms as England slumped to an innings defeat.

Root had been given a rousing reception from the SCG crowd when he came out to bat following the dismissal of Moeen Ali an hour into the day.

England confirmed the captain had picked up a viral gastroenteritis bug, moving to quash earlier suggestions his illness was related to the 42C temperatures the players sweltered through on Sunday.

Root arrives at the SCG, still wearing hospital wristband // Getty

Root also suffered a nasty blow on the finger late on day four but brushed off the pain and continued batting to see England to 4-93 at stumps.

England assistant coach Paul Farbrace confirmed after play on Sunday that Root's finger was "just sore" and spoke about how the tough Ashes campaign will help shape the 27-year-old as a leader in the future.

"He is very determined," Farbrace said.

"That's something although he's not scored the runs and the big hundreds he would've liked to have scored this series, the one thing he has done is try to apply himself and get stuck in and play as well as he possibly can do.

"His way of talking within the team is very much about application and getting stuck in and fighting.

Root gets treatment on his sore finger on Sunday // Getty

"Equally you need to back that up with a high level of skill in international cricket.

"We've seen in the dressing room, the way that he leads, the way that he speaks, the way he is around the team that he is growing into and is going to become a very good captain.

"He'll have learnt a lot in this series. He'll have learnt a lot in his short time as England captain.

"And he will only get better from that experience, because that is the nature of the person and we see that with his batting as well."

The best of Australia's march to Ashes glory

2017-18 International Fixtures

Magellan Ashes Series

Australia Test squad: Steve Smith (c), David Warner (vc), Ashton Agar, Cameron Bancroft, Usman Khawaja, Peter Handscomb, Shaun Marsh, Mitchell Marsh, Tim Paine (wk), Mitchell Starc, Pat Cummins, Nathan Lyon, Josh Hazlewood, Jackson Bird.

England Test squad: Joe Root (c), James Anderson (vc), Moeen Ali, Jonny Bairstow, Jake Ball, Gary Ballance, Stuart Broad, Alastair Cook, Mason Crane, Tom Curran, Ben Foakes, Dawid Malan, Craig Overton, Ben Stokes, Mark Stoneman, James Vince, Chris Woakes.

First Test Australia won by 10 wickets. Scorecard

Second Test Australia won by 120 runs (Day-Night). Scorecard

Third Test Australia won by an innings and 41 runs. Scorecard

Fourth Test Match drawn. Scorecard

Fifth Test SCG, January 4-8 (Pink Test). Scorecard

Gillette ODI Series v England

First ODI MCG, January 14. Tickets

Second ODI Gabba, January 19. Tickets

Third ODI SCG, January 21. Tickets

Fourth ODI Adelaide Oval, January 26. Tickets

Fifth ODI Perth Stadium, January 28. Tickets

Prime Minister's XI

PM's XI v England Manuka Oval, February 2. Tickets

Gillette T20 trans-Tasman Tri-Series

First T20I Australia v NZ, SCG, February 3. Tickets

Second T20I – Australia v England, Blundstone Arena, February 7. Tickets

Third T20I – Australia v England, MCG, February 10. Tickets

Fourth T20I – NZ v England, Wellington, February 14

Fifth T20I – NZ v Australia, Eden Park, February 16

Sixth T20I – NZ v England, Seddon Park, February 18

Final – TBC, Eden Park, February 21