The 34-year-old, who also played for Nottingham Forest, Leicester and West Brom, will say his final goodbye to fans in the Boxing Day clash at home to Plymouth.
He told the club's official website: "There comes a time when you have to call a halt. Whatever the temptation to go on and to try again, you can't ignore what your body is telling you.
"I've had a good career, it's been great. I feel it's better to be grateful for that rather than think about my regrets about not carrying on as a player.
"Although I won't be playing any more, I'm still going to be around the club and be part and parcel of it."