Australia's captain Michael Clarke has conceded he is far from guaranteed to be fit in time for the first Ashes Test in Brisbane next month, as his chronic back trouble grows increasingly stubborn.

Having been ruled out of the limited overs tour to India that precedes the home series against England, Clarke showed unusual pessimism about his fitness when discussing his chances of returning to full strength and flexibility in time for the Gabba.

There were grim tidings also from James Pattinson, who had originally hoped to recover from a back stress fracture he picked up in England in time to contend for a Brisbane pace berth.

Instead he admitted he was now well behind that schedule, and was looking at a place in the Perth Test as one of four fast bowlers as his earliest chance to resume in Test matches.

Since returning home from England, Clarke has undergone daily treatment on his back, and between now and the start of the Ashes the Australian team physio Alex Kountouris is readying himself to make frequent flights from Melbourne to Sydney to spend as much time as possible with his most pivotal patient.

However the process of constant work to strengthen Clarke has been progressing slowly, and there is always the danger of a relapse such as the one that curtailed his Champions Trophy campaign before the Ashes in England.

"There's certainly no guarantee at this stage," Clarke said at the national team's pre-season camp in Sydney. "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 who knows me very well, and he'd say there'd be doubt I won't be right. Making sure I'm doing everything I can to give myself the best chance ... plenty of rehab and recovery getting strength back in the areas that support my back. It's a lot of hard work but I'm willing to do the work to make sure I'm right for that first Test.

"Where I sit right now is I don't know when I'll be back playing cricket. We have no idea how long it's going to take. But in Australia I've got the physio in Sydney I've been working with since I was 17, I've got the machine, the medics machine that's helped me stay on the park for as long as I have through my career, and I'm in consistent contact with Alex Kountouris who will fly back and forth from Melbourne to Sydney to see me and make sure I'm improving."

Clarke's ideal preparation for the Gabba will be to regain full mobility in time to play in the Sheffield Shield matches scheduled to lead-in to the Ashes, granting him the chance to gain confidence and batting form before facing England's pacemen once more. "My best preparation has always been to play cricket and score runs doesn't matter what form of the game," Clarke said. "If I'm playing games of cricket and performing that helps me take it into one day cricket or test cricket. I probably train harder than what you have to do in game so playing is probably easier for me mentally and physically with the work that goes into it."

Pattinson had fought back tears when his Ashes campaign in England was ended during the Lord's Test by back pain that was revealed to be a fracture. While speaking more happily with the benefit of a few months in the recovery room, he is yet to resume running let alone bowling, and remains a long distance from fitness.

"I'm not even running yet which is not great," Pattinson said. "I get a scan in two weeks time which is a 12 week scan to determine whether the fracture has healed or not. Go from there, get results back from scan start running, should be fine. My back feels fine at the moment, I have no pain. Just a bit of a long process. I'm probably a month off bowling.

"I won't be back for the first Test, don't think I'll be right for the second ... but all things going well I could push for that WACA Test. If it's a bit green we could play four quicks up there, but 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 and last thing I want is for that to happen again and push my body too far and it's hard enough going through it once without going through it again. Long term is where I'm looking."