Ronaldo is set to rubber-stamp his world record switch to the Bernabeu before June 30, when he is expected to be unveiled alongside the Spanish club's other – galactico' signing, Kaka.
The Portuguese winger's move to Real has come at the end of a 12-month period when the 24-year-old did little to distance himself from speculation linking him with a move to the Spanish capital.
And McClair, who made over 350 first-team appearances for United during 1980s and 1990s, insists that Ferguson was right to part with a player who had made it clear that he viewed his future away from Old Trafford.
McClair said: "As far as the sale of Ronaldo to Real Madrid goes, Manchester United have been here before. Look back at the club's history.
"George Best, Eric Cantona and David Beckham have departed United in some shape or form and the club has continued to thrive and, in certain cases, has gone on to bigger and better things.
"A club as big as United is going to have big players and players move on. That9s a fact of football life.
"No one player is irreplaceable. Or to put it another way, nobody is bigger than the club. Selling Ronaldo to Real Madrid is good business.
"His comments in the past have intimated that he was not happy. There's no point keeping a player in that state of mind as it will eventually start to affect those around him." McClair is currently charged with identifying United's next generation of home-grown stars and the Scot believes that Ronaldo's departure can open doors for the club's promising youngsters.
McClair, speaking to championshipmanager.co.uk, said: "We move on.
United have always changed and adapted and that process is underpinned by the knowledge and experience possessed by the coaches and the manager.
"There are young players at the club who have benefited from that knowledge and experience.
"Now is the time for some of them who we have developed to see Ronaldo's departure as an opportunity."