News of his operation was made public by his old club, with a United statement cautiously optimistic about the prospects for the 76-year-old, the most successful manager in British football history.
Ronaldo, who considers Ferguson as a father figure has won major milestones under the former manager, including three premier league titles, one UCL title and also the first of his five Ballon d'Or.
Another added: "Very classy Tony much respect, great performance I hope you get what you want in the future". "Be strong boss xx".
Ferguson managed Scotland in the 1986 World Cup in Mexico following the death of Jock Stein, although he was unable to take his country past the group stage.
United's club captain Michael Carrick said he was "devastated" to learn his former manager had needed emergency surgery.
In the fickle modern game, which treats managers as disposable tissues, Ferguson was immovable Glaswegian granite for more than quarter of a century, re-establishing and then constantly re-inventing United's dazzle as the world's most celebrated club. "Thoughts are with the family and close ones". Ferguson's family requested some privacy regarding this matter.
Players past and present also showed their support to the former Manchester United boss who was at the helm of the Red Devils for 26 years.
"Everyone at Manchester United sends our very best wishes".
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However, Wednesday's match will have taken a lot out of the Merseysiders and I think that could prove crucial in this game. Olivier Giroud's victor , headed home before half time, puts Chelsea two points behind Tottenham and three off Liverpool .
Ferguson was pictured on the Old Trafford pitch last Sunday making a presentation to former managerial adversary Arsene Wenger, who is preparing to leave Arsenal after nearly 22 years.
Using the hashtag "legend", the athlete said: "Get well soon Sir Alex Ferguson my support are with family and friends.!"
During his managerial days, Sir Alex Ferguson split opinion across the globe.
Sir Alex remains in the thoughts of the footballing community as he recovers.
"The long-term consequences are quite hard to anticipate", head-way's Luke Griggs said.
FC Barcelona too wishes a speedy recovery for Sir Alex.
"We don't know exactly what kind of brain haemorrhage he had".
"We're all thinking of you, Sir Alex", the Gunners said on Twitter, alongside a picture of the pair from last weekend.