But the former England Under-21 international is hopeful of returning to action for the reserves in March with a view to returning to first-team contention before the end of the campaign.
"If I'm fit again and people think I can help the team then it would be great to be back in, but I'm under no illusions because I know it will be very difficult," he said.
"Six months is what people think a cruciate takes these days, but you can get little setbacks here and there.
"It's just a case of trying to get back into training when you're always going to a bit rusty and then there's obviously going to be a very good goalkeeper in front of me as well."