Celtic defender John Kennedy has been forced to retire from football on medical advice, the club announced today.
The 26-year-old defender came through the Youth Academy at Celtic Park and over the past 10 years made 45 appearances for the club, scoring one goal.
Kennedy told the club's official website, www.celticfc.net: "It is with great regret that I have made this decision. However, given the medical advice which I received, this is the right decision."
Kennedy continued: "Clearly, this is very disappointing for me and my family.
"However, this is something I will accept and come to terms with.
"I have enjoyed my time with Celtic immensely and I would like to thank everyone at the club and all the Celtic fans for all the support and backing they have given me during my time.
"It has been an absolute privilege to play for such a great club and of course I wish the team the very best for the future."
Kennedy's injury problems date back to his international debut for Scotland against Romania in March 2004, when he suffered a serious knee ligament injury following a challenge by Romanian striker Ionel Ganea, which kept him out of the first team for three years.
Several attempts at a comeback since then have failed, leading to today's decision.
Celtic manager Tony Mowbray said: "For John, his family and indeed everyone at the club, this is extremely sad news.
"John is a very fine footballer and a great man, someone who served Celtic with such determination and integrity and someone who had all the qualities required to become such a wonderful player.
"Indeed, he was already well down that path when he sustained such a terrible injury.
"I know that whenever he represented Celtic, he did so with a tremendous passion for the club and he was someone who gave his all in every game he played.
"It really is tragic that John's career has been cut so short in this manner. We will be giving John our full backing."
Celtic chief executive Peter Lawwell commented: "Everyone at the club is devastated at the news of John's retirement.
"John is a young man who has been an absolute credit to this club and someone who had one of the brightest futures in the game. We are all deeply saddened by this news.
"John is someone who fought his way through the Celtic ranks to become a first-team star - something which is a magnificent tribute to his talent and ability.
"No-one will ever forget how he performed in the Nou Camp that famous evening back in 2004 and no-one will ever forget how he was so cruelly injured in his prime.
"We thank John for everything he has given us - the club will be doing all it can to provide John with as much support as possible."
Scotland boss George Burley, in Cardiff for tomorrow's friendly against Wales, added his sympathies.
He said: "It's really sad for the boy. This is a big blow to John, his family and everyone who knows him.
"He's been through a lot of heartache over the years. At one point he was one of the most promising defenders Scotland had.
"You never know what can happen in football, it shows you the ups and downs of a footballer. Whatever career he decides on, we wish him all the best."