Considered the most successful manager in the history of British football, Ferguson won 38 major trophies in just over 26 years in charge of Manchester United, including 13 Premier League titles and the UEFA Champions League twice.
It is a measure of the Scot's success on the pitch, and his stature off it that tributes poured in from around the world of sport, and beyond, to wish the 76-year-old a speedy recovery after he underwent surgery on Saturday.
"Everyone at AC Milan wishes Sir Alex Ferguson a full and speedy recovery," said a statement by the seven-time European champions on their official Twitter page early Sunday morning.
Juventus coach Massimiliano Allegri, who is on the verge of leading the Turin giants to a seventh successive Serie A crown, said: "Stay strong Alex Ferguson."
News of Ferguson's condition also had an impact beyond the world of football.
Top American baseball side the Chicago White Sox posted a heartfelt message on their Twitter page weeks after one of their players, Danny Farquhar, recently suffered a brain haemorrhage while sitting in the team dugout.
"The stand with the community in sending our positive thoughts to Sir Alex Ferguson," said the message on @whitesox.
"Having been recently impacted by a brain hemorrhage in our own family, we know the dramatic impact it causes, and the strength that can be drawn from those who care."
Ferguson, who retired from management five years ago, appeared in good health when presenting a commemorative vase to old rival Arsene Wenger, who is stepping down as Arsenal manager, at United's Old Trafford ground last week.
But on Saturday an ambulance was called to the Scot's home in Cheadle, near Manchester, at 9:00 am (0800 GMT).
Concerns for Ferguson's health mounted when it was announced his son, Darren, the manager of English third-tier club Doncaster, would miss his side's match against Wigan because of "family reasons".
News of Ferguson's operation was made public by United in a statement that appeared to be cautiously optimistic about his prospects for recovery.
"Sir Alex Ferguson has undergone emergency surgery today for a brain haemorrhage," the statement said on Saturday.
"The procedure has gone very well but he needs a period of intensive care to optimise his recovery. His family request privacy in this matter.
"We will keep Sir Alex and his loved ones in our thoughts during this time, and we are united in our wish to see him make a comfortable, speedy recovery."
Pending updates on Ferguson's condition on Sunday, messages of support from all walks of life poured in.
"I wish Sir Alex Ferguson a speedy and full recovery," said British Labour MP John McDonnell, the Shadow Chancellor.
"A brilliant manager and a good man, who won the respect of all of us football supporters worldwide."
Wenger, who spent many years as Ferguson's main managerial rival in England's Premier League, offered his support to the Scot in a short statement to the Daily Mail on Sunday.
"I am concerned and I’m thinking about him and his family," said the Frenchman.
"I trust his strength and his strong character will get him well very quickly."