Steve Smith in massive doubt for third Test after sickening blow

Australia and England's captains expect Steve Smith will be fit for the third Ashes Test, but the concussed superstar's reality is he will almost certainly remain on the sidelines.

Smith has made history throughout his remarkable run-laden career but on Sunday he did so in a fashion that no player would ever want.

The former skipper was on the wrong end of international cricket's first concussion substitution, a policy the sport introduced at the start of this Ashes.

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Smith woke up with a headache and other concussion symptoms on day five of the drawn second Test at Lord's, having passed several tests on day four after being hit on the neck by a Jofra Archer bouncer.

Marnus Labuschagne claimed Smith's place in the XI had played a key role in Australia's successful stonewall, facing more balls than any of his teammates.

Both camps will now quickly turn their attention to the Test that starts in Leeds on Thursday, with all eyes on Smith.

There is no mandated minimum time on the sidelines beyond the initial 24 hours but given the gradual steps Smith must take it would be staggering if he completes a miraculous recovery in such a short period.

Tim Paine, who was among the players to express skepticism about the new rule prior to the first Test, is nonetheless upbeat.

"I reckon it will be tough to stop Smithy walking out," Paine said.

"I haven't been to university, so I'm taking the advice - as Steven is - from our doctors.

"He'll be reassessed in the next few days, probably constantly I would imagine.

"Cricket Australia have pioneered the concussion sub and it is something they take very seriously, I know our doctor does."

Smith is also hopeful of being fit for the next Test.

"But it's certainly up to the medical staff," Smith added.

"Concussion is an area of concern and I want to be 100 per cent fit."

England skipper Joe Root described the moment that Smith hit the deck, face first, as "horrible".

"You never want to see anyone get hurt," Root said.

"I couldn't believe he came back out but he was desperate to do well for Australia and his teammates.

"We'll plan for him to be ready to play and keep trying to find ways to get him out."

Smith had no issues with being withdrawn from the second Test, calling it the "right decision".

Smith defended coach Justin Langer and team doctor Richard Saw for letting him bat on Saturday after the frightening blow that dredged up memories of Phillip Hughes' death.

"I passed all the tests and felt fine, felt normal," Smith said.

"They (Langer and Dr Saw) were both happy and I was comfortable as well."

Paine hints at batting changes

Paine also refused to rule out changes at the top of the order for the third Test after David Warner and Cameron Bancroft flopped again at Lord's.

Warner scored three and five in the second Test and has now registered four successive single digit totals in the series - the first Australian opener to do so against England since Mark Taylor in 1997.

Bancroft took an amazing catch at short-leg to dismiss Rory Burns but his technique has been severely tested by the England bowlers and scored just 16 on Sunday after registering 13 in Australia's first innings.

The West Australian is under huge pressure to keep his spot in the team, especially after Labuschagne’s superb knock.

Paine admitted Labuschagne would be in the mix for a start in Leeds - regardless if Smith is cleared to play - with Usman Khawaja potentially being promoted to the top of the order.

"Of course he is, so is Marcus Harris," Paine said.

"We know Marnus is a quality player and he's getting better all the time. We're happy with the way he played.

"But I think if you look at top order batting across the two teams it shows you it's probably a pretty difficult place to be batting on either side.

"We know how good David is, he's got 7000 Test runs at 50 and Cameron Bancroft I thought in this game looked pretty good, faced a lot of balls.

"He would've liked to have scored a few more runs but I thought he acquitted himself pretty well again against some pretty high-quality bowling."

Paine also hinted at possible changes to the bowling attack despite Peter Siddle, Josh Hazlewood and Pat Cummins all bowling well at Lord's.

James Pattinson, who bowled so impressively in the first Test, was rested for the second and Mitchell Starc, who played at Headingley for Yorkshire in a county cricket spell six years ago, is also waiting in the wings.

"As we've said throughout the series so far we'll get to Leeds, have a look at the conditions and pick the best team to win the game and take 20 wickets," he said.

"Whether Steve's playing, whether James Pattinson is playing it doesn't matter.

"The players we pick are picked to play a role, they're really clear on that."