Captain Clarke mulls declaration in first Test

Australia are yet to reveal their plans for a potential declaration on the morning of day three of the first cricket Test against India.

Michael Clarke (128) and Steve Smith (162 not out) shared a 163-run stand at Adelaide Oval on Wednesday, lifting Australia to a score of 7-517 at stumps after a rain-marred second day.

Pundits were tipping Clarke would declare late on day two, but he instead opted to amass a bigger total.

Smith suggested on Wednesday night that Clarke had yet to disclose his thoughts.

"Not too sure," he said.

"I think the skipper's going to sleep on it, to see if we come out straight with the ball or bat for a little bit longer."

Smith and Clarke were particularly aggressive during the final session on Wednesday.

"We said we wanted to get to 500 so it was about putting the accelerator on and trying to get a few boundaries away, so it worked out well," Smith said.

Clarke batted in great pain and with little freedom due to a flare-up of his chronic back injury on day one, when he retired hurt on 60 and was rushed to hospital for scans.

The 33-year-old donned a back brace while batting on day two, his short-term future still uncertain due to the three degenerative discs in his lower back.

"In the breaks he was getting a bit of treatment, he was waking around, trying to stay as active as he could," Smith said.

"Sitting down's probably the hardest thing for him with his back. He was trying to stay quite active."