Nathan Lyon on Monday backed David Warner to open the innings for Australia against India in the third Test this week, saying he had the "X-factor" to change a game.

The explosive opener missed the first two Tests with a groin injury, but has been training and was included in the squad for Thursday's crucial clash in Sydney, with the four-Test series locked at 1-1. Warner said over the weekend it was "highly doubtful" he would be fully fit, voicing concern he might struggle with his range of shots and not be able to perform in the field at slip to his usual high standards.

But off-spinner Lyon said it was worth taking the risk. "One hundred percent. I think David is an X-factor," he said.

"He is a world-class batter, we all know that, so I am 100 percent expecting David to go out there in the next couple of Test matches and do well. Obviously, he's got all of the support of the Australian changing room and everyone else around the world to come in here and do well," he added. "So I'm looking forward to getting Davey back up to the top order for Australia."

Warner will open the innings if selected, but who pads up alongside him remains to be seen with Joe Burns dumped after a string of poor scores.

Will Pucovski could make his debut after a concussion scare, selectors may opt for Marcus Harris or even stick with Matthew Wade who filled the role in Warner's absence.

Lyon is eyeing the personal milestone of his 400th Test wicket in Sydney, he currently has 394. He could then mark his 100th Test appearance in the final match of the series in Brisbane next week.

"If I can play my role and make sure we can win this series against a pretty amazing Indian cricket side, those milestones will be nice to look at come the end of my career," said the 33-year-old. "It's pretty amazing that I've got a couple of them just around the corner. But for me it's more about coming out and playing my role, and hopefully we can sing the (team victory) song twice and that will top off my milestones."

Crowds at the Sydney Cricket Ground will be reduced after capacity on Monday was cut to 25 percent, around 9,500 fans per day, from 50 percent because of a coronavirus outbreak in the city.

"Reducing the capacity of the venue is crucial in achieving social distancing requirements," said Cricket Australia interim chief Nick Hockley.