England have confirmed Jake Ball as their fourth seamer for the first Ashes Test in Brisbane.
Ball takes the final place in an England line-up which has otherwise been inked in for several weeks.
It will be the 26-year-old's fourth Test cap, but first in an Ashes series, following his recovery from a sprained ankle suffered in England's second warm-up match in Adelaide two weeks ago.
Ball has not played since but was declared fit for selection on Monday.
Sky Bet first Test odds: Australia 8/11, England 11/4, draw 7/2. Click here for all markets
Root explained, in an interview on the England and Wales Cricket Board website ecb.co.uk, why Ball had inched the verdict ahead of Craig Overton.
"It wasn't an easy decision," he said.
"Craig's come into the squad, and everything that's been asked of him he's done brilliantly well.
"But Jake has bowled well when he's had his opportunities on the tour, and I think the way he goes about things on these surfaces could be really challenging for the Australians."
England's medical staff are satisfied Ball has fully recovered from the injury he suffered when he lost his footing in his delivery stride in the second of three warm-up matches.
"Yes, he wouldn't be playing if not," said Root.
"He's worked really hard and done everything he can to make sure he's in top shape for this first Test."
Australia, meanwhile, have added Glenn Maxwell to their squad as cover for David Warner - even though the opener remains confident he will be fit to face England.
Warner cricked his neck taking a high catch in fielding drills on Tuesday.
A day later, though, his captain said: "Davey's going well.
"He's just had a hit ... he's very confident, and he says he's good to go.
"I think he's improved a fair bit over the last 24 hours. We hope he can continue improving and be 100% at 10 o'clock in the morning."
Teams for the first Ashes Test, starting in Brisbane on Thursday at 00.00 GMT:
England: JE Root (Captain), AN Cook, MD Stoneman, JM Vince, DJ Malan, MM Ali, JM Bairstow (wkt), CR Woakes, JT Ball, SCJ Broad, JM Anderson.
Australia (probable): S Smith (Captain), D Warner, C Bancroft, U Khawaja, P Handscomb, S Marsh, T Paine (wkt), M Starc, P Cummins, N Lyon, J Hazlewood.
Umpires: A Dar (Pak) and M Erasmus (SA).
