'Stretch' Calls it a Day
"Stretch" who was a loyal servant to the Blades following his £100,000 transfer was diagnosed with multiple sclerosis in late 2009, and now believes he's unable to continue in the game.
'Obviously this has been a very difficult decision, I absolutely love football but this is the right thing for me to do now,' Armstrong told the club's official website. 'It's right for me professionally, medically and also personally.
'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.
'There are so many games, every single one is played at a high tempo, it's very hard to perform week in and week out. I know I gave it my best shot but ultimately I was not physically able to do it.
'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.'
Armstrong suffered a near crippling injury shortly after his transfer, but following over a year out of the team, and after almost having to have a leg amputated, the full-back returned to the side where he would make over 100 appearances, including 28 in the Premier League.
He rotated positions under Bryan Robson, before joining Reading in 2008 where he won the player of the year award in his first season.
He will be best remembered by Blades fans for his excellent goal in the 3-1 win at Hull during the Blades promotion season, and the pinpoint cross which allowed Ade Akinbiyi to smash home in the 2-1 win over Sheffield Wednesday at Hillsborough.
Armstrong's current boss Brian McDermott added: '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 absolutely sums up everything that is good about human beings. Nobody could have tried harder and given more than he has given.
'It is important that Chris knows that I personally, and I am sure I can speak for all the staff and players, will always be there for him any time he needs us.'