The Scottish tactician will step down from his role as Manchester United manager at the end of the season after 26 years at the helm and his outstanding success has not been lost on Ibrox boss McCoist.
"His like may never be seen again. Sir Alex has been a colossus and his achievements might never be surpassed," said McCoist.
"He has been at the very pinnacle of the game for so many years and seemed to get better with age. His defeats always seemed to make him stronger and he always bounced back to reach another height.
"But while his total dedication and intense will to win were always obvious Sir Alex also had a sharp sense of humour. When I heard about his decision I sent him a text saying: 'Gaffer, I hope this isn't an over-reaction to Monday's result when Rangers Legends beat Manchester United Legends 4-1'.
"Sir Alex, who built team after team, and not only on the pitch, will be sorely missed by the game.
"Time and again he proved himself a football genius with no equal. We all wish him well, the players, the staff and the fans.