Celtic manager Gordon Strachan has expressed his regret that midfielder Roy Keane has opted to retire from football. Strachan was Keane's last manager as a player and the Scot feels it is a shame that injury has cut short the career of a man he described as: "one of the greatest-ever players to grace the game of football." In a statement released by Celtic, the Bhoys chief added: "It was fantastic that we were able to bring him to Celtic and it has been a privilege to work with him.