Former Manchester United coach Alex Ferguson, one of the greatest managers in football history, underwent surgery Saturday for a brain hemorrhage, according to a tweet from the team's verified Twitter account.
Since retiring from United after nearly 27 years in charge in 2013, the 76-year-old Ferguson has continued to attend matches at Old Trafford, participate in coaching initiatives, and has been a regular at horse racing as a prominent owner.
These include 13 League titles and 2 Champions League trophies.
Manchester City said it wished Ferguson "a full and speedy recovery after his surgery".
Another added: "Very classy Tony much respect, great performance I hope you get what you want in the future".
Footballers who used to play for the legend wrote about him on social media.
Manchester United captain Michael Carrick said he was "absolutely devastated", while goalkeeper David De Gea said he was praying for his former manager.
Southampton manager Mark Hughes, a United striker during Ferguson's early years at Old Trafford, said: "I only just got a little whisper earlier on".
Scott McTominay: Thoughts & prayers are with you and your family boss. His family therefore request privacy in this matter. The children of players and staff who played and worked under him still receive birthday and Christmas presents from Ferguson and his wife Cathy.
There was no further update on his condition on Sunday evening, although his former club Manchester United thanked the football community for its expressions of concern.
Some referred to the strength of character Sir Alex has shown through his life, with Paul McGrath stating: "My prayers and thoughts are with him and his family".
Many of his former players, including Cristiano Ronaldo, Wayne Rooney have sent their best wishes - David Beckham's told his old boss to "keep fighting".
Diego Forlan: My thoughts and prayers go to Sir Alex Ferguson and his family on these tough moments. "Every brain injury is unique, as is every individual's recovery".
Ferguson retired five years ago having won a 38 major trophies in just over 26 years in charge at Old Trafford.
Luke Griggs, of the brain injury charity Headway, said a brain haemorrhage can occur spontaneously as a result of a ruptured aneurysm, or from a blow to the head, even a minor head injury.
FC Barcelona too wishes a speedy recovery for Sir Alex.