Armstrong joined Reading from Sheffield United in August 2008
Reading defender Chris Armstrong has been forced to retire from football at the age of 28 after succumbing to Multiple Sclerosis.
Armstrong was diagnosed in December 2009, but had managed to make seven appearances for the Royals this season.
"Obviously this has been a very difficult decision," said the former Bury, Oldham and Sheffield United man.
"I absolutely love football but this is the right thing for me professionally, medically and also personally."
Armstrong added: "With the illness, both the medical team and I didn't feel I could regularly perform to the level you have to in the professional game.
"I've been very fortunate to play for Reading and all my other clubs, I've been lucky to have a career that I know many people would be delighted to experience. I'll miss being a part of the game on a daily basis."
Reading manager Brian McDermott said: "Chris has been an inspiration to me.
"Over a long period I've had many conversations with him. He's a quiet, unassuming man who sums up everything that is good about human beings. Nobody could have tried harder and given more than he has given."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.