Steven Smith has said that Ishant Sharma's absence for the Test series in Australia will be a "big loss" for India, but also conceded that David Warner missing at least the opening match in Adelaide will be a challenge for the home side's depth.

There could be a vulnerability at the top of the Australia order for the India bowlers to exploit with Warner out of Adelaide due to his groin injury, Joe Burns struggling for form and uncertainty over who the opening pairing will be after Will Pucovski suffered concussion from a blow to the helmet against the Indians in the first tour match.

One of the more unlikely routes Australia could take to plug the gap would be to promote Marcus Labuschagne to open, which could also create a route for in-form allrounder Cameron Green in the middle order, and Smith backed Labuschagne to have the game to fill the role if needed.

"I think our depth is obviously going to be tested with Davey out and a few potentially new players coming in," Smith said. "It'll test us out no doubt against a good Indian outfit. We know how good they are at Test cricket. They beat us out here last time and they're a very good side."

"When you bat at No. 3 you are sometimes in second ball of the game, that's the reality of batting there so, someone at three could certainly go up the top."

Ishant, who took 11 wickets at 23.81 on the previous tour to Australia, was ruled out of the series late last month following the abdominal injury he picked up at the IPL. Though he has recovered the problem was getting him ready for the demands of Test cricket and also the difficulties presented by the need for two weeks quarantine on arrival in Australia.

"It was difficult with sitting on the sidelines and not being able to go out there and make a difference, that was the toughest thing to me knowing I probably could make a difference if I was out there." Smith on missing the India series in 2018-19

India will still be able to field Jasprit Bumrah and Mohammed Shami, who were both central figures in their 2018-19 series victory, with Umesh Yadav shaping as the likely third quick following a strong outing against Australia A at Drummoyne Oval. Bumrah and Shami are set to play their first game of first-class cricket since the beginning of March in the day-night warm-up match against Australia A from Friday.

Asked whether this could be considered India's strongest-ever attack, Smith singled out the absence of Ishant. "They're experienced now, particularly Shami and Bumrah," he said. "Ishant Sharma is probably a big loss for them...he's played a lot of cricket now and is a good bowler. Without him it may not be their strongest because I'm sure they'd like him to play, no doubt.

"Shami's played a lot of cricket, Bumrah's played a reasonable amount of cricket and is a quality bowler. Whichever spinner they use - Ashwin, Jadeja, Kuldeep - we'll wait and see there but they've all played a fair bit of cricket now. They're all good bowlers and we're going to have to be at our best if we're going to beat them."

Smith was not part of the 2018-19 series as he served his ban for the Newlands ball-tampering episode and this series will be the first time he has faced Bumrah in long-form cricket. In white-ball internationals he has faced Bumrah on 14 occasions, and been dismissed by him just one, and at the IPL they have come against each other 10 times with Bumrah removing Smith on three occasions.

"His skillsets won't change too much," Smith said. "We know how he bowls, he's got good pace, he's got that awkward action, very different to a lot of people so you've got to be pretty watchful all the time and he's a quality bowler, I'm excited to be coming up against him in this series. You like to be coming up against the best and he's certainly up there with them."

Smith admitted he found it tough to follow the series two summers ago as he served his time away from the game. "I watched bits and pieces. It was difficult with sitting on the sidelines and not being able to go out there and make a difference, that was the toughest thing to me knowing I probably could make a difference if I was out there. That was hard, but it's an exciting series coming up."