Carle hasn't played since rupturing his anterior cruciate ligament playing for the Sky Blues against Melbourne Victory in an A-League match in December, 2014.
His initial recovery went well, but once he started running again his knee reacted badly and the problem hasn't gone away.
Carle, now 34, admits time is running out for him because he is only interested in going out with a final fling in the A-League and the longer his absence from that level the less likely it is he'll receive offers to return.
"The ideal scenario for me was to play until I was 35," Carle said. "That would have been a 20-year career for me.
"Things often don't go to plan in football, but I haven't retired yet. I'm still doing everything possible to get back, but the longer it goes the less likely it is that I'll play again, you know.
"I've been out of the game for 16 months and I haven't been able to train. The first three months I was able to do proper recovery and then after I started running again and the problem emerged it's been complete rest, so I haven't really trained for over a year now.
"I started swimming and biking again six weeks ago, but trying to get from there back to a level with the young guys running around, I don't know. I always wanted to go out playing, not forced to retire with an injury, but we'll see how it goes."
Carle said he had been in regular contact with doctors in a bid to find a remedy.
"I was doing really well early on in my recovery, but when I started running again I got bad pain," he said. "It was bone bruising and there's nothing you can do about it. All you can do is rest it and see when it gets better. I ask how long and it's like: 'How long's a piece of string?'
"I went to see a bone specialist recently and he's looking at ways of trying to speed it up. I'm going through a process with him to see if there's any medication that will help the bone heal.
"A small percentage of people get this sort of problem when they start running again after a reconstruction. After such an operation the knee isn't like it was before. It could have been something I did when I tore the ACL, but you don't know until you start running on it.
"I've been told the operation was a success and I did nothing wrong in the recovery. I've just been very unlucky, like a minority of people who get this problem."
Carle made his debut in the old NSL as a 15-year-old for Sydney Olympic, in 1997. He went on to become one of the most popular players in the A-League because of his immense skill, unselfishness and great personality. He also played in England with Bristol City and Crystal Palace.
Asked if he would be prepared to play at a lower level than the A-League just to get back on the field again, Carle said he wouldn't want to take a spot in a team that could go to a young player coming through.
"All due respect to the other leagues, but if I play it'll be in the A-League," he said. "If I wasn't good enough to play at A-League level anymore I'd retire and just have a kick-around with my friends and play with the kids in the backyard.
"I'm not saying my view's right or wrong, but, personally, I think the NPL is more for the young kids, wanting the chance to get into the A-League, and I wouldn't want to take that opportunity away from someone by coming in as an ex-pro.
"I might be taking some young guy's opportunity to shine and get himself a chance in the A-League.
"I'm hoping I get a bit of luck with the bone specialist and there is some medication they can put me on. I've had an MRI and a few other tests and I'll get all the results when I see him next, on Friday. We'll see where it's all at then."