The 33-year-old, who won 41 caps during his England career, has endured a series of setbacks since playing his last match for Blackburn last December.
He underwent a back operation after suffering from sciatica - a set of symptoms caused by irritation of the sciatic nerve - and was then struck down by something which was potentially far more serious.
"I had a back operation," he explained on Goals on Sunday. "I was suffering awfully with sciatica down my sciatic nerve in my leg and I had a microdiscectomy early in March - basically a small part of a disc was removed from the bottom of my back.
"The operation was brilliant but five days later I went back home and started coughing up blood.
"Gradually my chest was getting tighter. I went to hospital and got a scan. They told me that I had a blood clot on my right lung.
"I think there was a very, very small percentage of a chance that it could have happened and I was just unlucky.
"They have still got to do the research on where it came from and what happened. Obviously they can't at the moment because I am on the warfarin tablets, which thins my blood and would affect the test.
"But I have been given a date when I can come of those - September 3. A week after that hopefully they will be completely out of my system and I can train. So hopefully before Christmas you will see me playing again."
The former Leeds and Tottenham stopper has returned to some aerobic training but is still prevented from full-contact work. Although, he hopes his injury and illness nightmare may soon be over.
"I have been back at the training ground, running, swimming and biking for the last two or three months," he said. "But it gets a little bit frustrating.
"I've been amongst the lads, not being able to put my gloves on because the warfarin is what stops me doing contact. If I got a bleed or a bruise it would be a lot more serious than anybody else's."