Australian captain Michael Clarke is defying a “significant back injury” by returning to bat against India on day two of the first Test in Adelaide.

Clarke retired hurt on 60 on Tuesday’s opening day with a flare-up of his chronic back injury.

The skipper, who has three degenerative discs in his lower back, was sent for scans and had injections to soothe inflammation.

Clarke strode onto Adelaide Oval for Wednesday’s day two with Steve Smith (72 not out) despite Australia’s team physiotherapist Alex Kountouris admitting the captain was “struggling”.

“Unfortunately it’s quite a significant back injury,” Kountouris said before play.

“He hasn’t had anything like this for 18 months, the last time was at the Champions Trophy in England.”

Clarke was able to resume his innings at the start of play halted when a wicket fell in the final over on Tuesday.

The skipper overcame a recurring left hamstring injury to play the rescheduled first Test.

But Kountouris believed his current woes were unrelated to the hamstring issue.

“This is his right lower back. This is his old injury, what he’s had in the past,” he said.

“I don’t think it’s directly related to his hamstring, because it’s the other side.

“We believe it’s related to his old disc injuries. With that comes a lot of muscle spasms and other things that cause pain.”