Set to return in Test cricket against India for the Perth Test on Friday, Australian paceman Ryan Harris is wary about breaking down again and said that he had "bad thoughts" about his recurring injury problems.

South Australian right-arm fast bowler Harris has all but been assured of selection in the playing eleven for the third Test at the WACA.

"Of course I am nervous about things. In the back of my mind, I do know that things could go wrong for me in Perth. With what has happened to me with injuries in the past, I have had some bad thoughts go through my mind about what could happen and what could go wrong," Harris said.

"I've woken up at night a few times thinking about things. But it has been a matter of clearing those bad thoughts from my mind," he added.

The 32-year-old Harris finds himself in a make-or-break situation given the swathe of fine young bowlers like James Pattinson and Patrick Cummins are at the forefront of Australia's plans for the future.

Harris, who returns from a pelvic injury as well as managing some nagging knee and back issues, realises that if he breaks down again he is unlikely to get another chance at the Test level.

However, the pacer sounded confident ahead of the crunch game and said he has enough match fitness to continue India's Test misery.

"I might not have played a four-day game in my return but I've played a bit in the Big Bash and I've been going pretty well. When I think about it, I know I have done the work and got the miles in my legs," he was quoted as saying by Daily Telegraph.