Crerand pities Ferguson's successor, claiming his fellow Scot will be a tough act to follow.
"I'm just stunned," said the 1968 Manchester United European Cup winner. "God help the poor fellow who's going to have to follow him because the standard he has set is incredible."
Crerand suspected Fergie was planning his farewell when he signed Robin van Persie last summer.
"I thought when Sir Alex signed Robin van Persie that he never buys players at the age of 29 and I thought maybe he bought him as he wants to go out by winning the league," he said.
"It entered my head, but then I forgot about it as I thought he would want to win the European Cup."