United confirmed the 76-year-old's situation in a statement on Saturday after reports had begun circulating that he was in intensive care.
In a statement on Sunday evening, Manchester United said: [We] would like to thank its friends in the wider football world for the countless messages of support that have been conveyed following the news that Sir Alex Ferguson underwent emergency surgery on Saturday evening. "His family request privacy".
During his 27 years at Old Trafford, he won 13 Premier League titles, five FA Cups, four League Cups and the champions League on two occasions.
"We will keep Sir Alex and his loved ones in our thoughts during this time", United tweeted, "and we are united in our wish to see him make a comfortable, speedy recovery".
Chelsea manager Antonio Conte has joined an ever-growing list of football figures in wishing Sir Alex Ferguson a speedy recovery following his brain haemorrhage. "Sending prayers and love to Cathy [Ferguson's wife] and the whole family".
He famously won the Treble of Premier League, FA Cup and Champions League in 1999, the year in which he was knighted. Manchester United then confirmed the unfortunate news about their former boss.
Glasgow-born Ferguson is one of the most successful managers in the game.
"You really think Sir Alex is indestructible". "Thoughts are with the family and close ones".
Sir Alex's son Darren, manager of League One side Doncaster, did not attend his side's final home game of the season against Wigan due to his father's illness.
Sir Alex had been known for his fighting spirit and never-say-die attitude and there's many who hope that will serve him well in his recovery.
He said: "Every brain injury is unique, as is every individual's recovery".
The club's Spanish goalkeeper, David De Gea, tweeted two prayer emojis for his former manager.
Here's hoping Sir Alex pulls through!
Ferguson has been married to wife Cathy since 1966.