SYDNEY - Australian captain Michael Clarke on Thursday admitted he may not be fit for the first Ashes Test against England next month, with his long-standing back problem needing extended treatment and rest.

Clarke was ruled out of Australia's one-day tour of India this month and while desperate to be ready for the first Ashes Test in Brisbane on November 21, the star batsman is pragmatic. "Where I sit right now is I don't know when I'll be back playing cricket," he said. "We have no idea how long it's going to take. "There's certainly no guarantee (for the first Test) at this stage. It's hard for me to say that because I'm trying my best not to look at it like that.

"I'm always positive and if they ask me, I'll say I'll be fit in a week's time. But you ask Alex (Kountouris, team physio) who knows me very well, and he'd say there'd be doubt I won't be right." Clarke has been plagued by back problems for years and they flared up again before Australia's final ODI in Southampton last month at the end of a gruelling five-Test Ashes tour to England, which Australia lost 3-0. He played in that game, but selectors were reluctant to take any more risks given the big home summer coming up, and ruled him out of the India tour, with Kountouris warning of an "extensive rehabilitation period before returning to competitive cricket".

Coach Darren Lehmann said all he could do was hope Clarke would be fit to face arch-rivals England, who are bidding to win a fourth straight Ashes series -- something they last achieved in the 19th Century. "I hope he improves his back pretty quickly," Lehmann said. "(The Ashes) is a long way off so hopefully with all the medicos behind him getting it right he should be right.

"But only time will tell. I can't worry about that. What I can worry about is making sure all the other players are ready to go as well... getting the right side for the first Test match." In a further blow, fast bowler James Pattinson also revealed he had no hope of being fit for Brisbane as he battles a back stress fracture, with the third Test in Perth seen as his likely earliest return. "I won't be back for the first Test. I don't think I'll be right for the second," said Pattinson, who broke down after the Lord's Test in July.

"But all things going well I could push for that WACA Test. I'll know more when I start bowling. I'm probably rushing a bit if I'm trying to get back for that first Test."

Australia are due to play five Tests against England, starting in Brisbane, with their fast bowling stocks already depleted. Mitchell Starc and Pat Cummins are both expected to miss the Ashes with back injuries and Jackson Bird also under a cloud. The England Test squad is due to arrive in Perth on October 25.