Celtic defender John Kennedy has been forced to retire from football on medical advice, the club announced. The 26-year-old told the club's official website: "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.
Several attempts at a comeback since then have failed, leading to Friday's decision.
Celtic boss 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."