A slipped disc earlier in his career has returned to irritate Parnaby, who has suffered sleepless nights due to the pain of his latest setback.
The pain is not the only aspect keeping the Blues defender awake at night, as he admits his long-term future has been playing on his mind.
"This is the most worried I've ever been about an injury," Parnaby told the Birmingham Mail.
"The first thing that enters your head is that will it be a long-term problem. I know that it's a bad way to think but that's just the way it is.
"I've been thinking how long will I be able to stick it. It's something that has been lying idle for a while, it was years ago when I first did it.
''I slipped a disc and had another disc pushing on to a big nerve that runs down my back. It gives you irritation in other places but I had just a big spasm in my back for a week or two.
''I had an injection to sort it out and hopefully that will settle it for a while and get me through the rest of the season.
"I couldn't sleep for a week, it was ridiculous. When it's on the nerve it affects everything but the doctor sorted me out with some decent pills, which helped me out a bit.
"Fingers crossed, I can just keep doing my exercises as much as I can and strengthen it as much as I can. Then I might be able to get away with it.
"Now I feel more confident, I'm moving around quite well now and I've just got to be patient then hopefully it will sort itself out."