Alex Ferguson has undergone emergency surgery for a brain haemorrhage, according to UK football club Manchester United.
In a statement issued on Saturday, the club said the procedure had gone "very well" but that the former manager would need "a period of intensive care to optimise his recovery".
"His family request privacy in this matter."
United captain Michael Carrick tweeted: "Absolutely devastated to hear about Sir Alex being unwell in hospital. All my thoughts and prayers are with him and his family. Be strong boss."
Ferguson, 76, was Manchester United's manager from 1986 to 2013 and led the club to victory in two Champions Leagues, 13 Premier Leagues and five FA Cups.
He made his reputation as a manager in his native Scotland with Aberdeen.
Nicola Sturgeon, the first minister of Scotland, said on Twitter: "My thoughts are with Alex Ferguson and his family - wishing him a full and speedy recovery."
