Manchester United said in a statement: "The procedure has gone very well but he needs a period of intensive care to optimise his recovery".
It comes after son Darren Ferguson skipped his Doncaster side's League One match against Wigan Athletic on Saturday.
"So we hope that he makes the full recovery and all our regards are with him and his family".
Liverpool manager Jurgen Klopp admitted he could not believe the news which emerged on Saturday evening after bumping into Ferguson recently. Everyone thinks it was all this "hairdryer", but the boss enjoys a good time, really enjoys his racing and is good company when you're around him.
"So a big hug and our thoughts are with his wife Cathy and the Manchester United family".
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During his managerial days, Sir Alex Ferguson split opinion across the globe.
Ferguson was at Old Trafford last Sunday when he presented departing Arsenal boss Wenger with a commemorative trophy. Most impressively, perhaps, is the two Champions League titles. Thoughts with all the family.
Guardiola then invited a former assistant of Ferguson's, Brian Kidd, who is now part of City's coaching staff, to lead the tributes from their Manchester rivals.
Manchester United forward Jesse Lingard said: "Thoughts and prayers sir alex", left-back Luke Shaw tweeted: "Sending my love and best wishes to sir Alex", while former goalkeeper Peter Schmeichel wrote: "Please Be strong Win this one".
Everyone was shocked when the news came out and everyone is still hoping the United icon will be able to pull through by showing the fighting spirit everyone has associated with him once more.
He famously won the Treble of Premier League, FA Cup and Champions League in 1999, the year in which he was knighted.