Sir Alex Ferguson has been taken to hospital after feeling unwell at Old Trafford before Manchester United's game against Liverpool.
Sky Sports News understands he is conscious and has had precautionary checks.
Sir Alex, 84, is a regular at Manchester United matches both home and away, having managed the team for nearly 27 years until his retirement in 2013.
He joined the Red Devils in 1986 and was in charge for 1,500 games, leading United to 13 Premier League titles, five FA Cups and two Champions League triumphs.
He then served as an ambassador for the club until 2025.
Earlier on Sunday, Sir Alex was pictured on social media at the stadium.
Dr Aseem Malhotra posted a photo on X of himself with the former United manager.
The British cardiologist, who is an adviser to US health secretary Robert F Kennedy Jr, was criticised last year after claiming at Reform's annual conference that COVID vaccines were likely a "factor in the cancers in the Royal Family".
The UK's health secretary Wes Streeting said in September that "these anti-vax lies have consequences" and had led to the return of diseases such as measles and whooping cough.
United won Sunday's match against Liverpool 3-2.
Interim United manager Michael Carrick told reporters that he was aware of Sir Alex Ferguson becoming unwell before kick-off and he was "affected" by the news.
Carrick added he hopes that when Sir Alex hears about the result, it will give him a "boost".
In his illustrious career, Six Alex claimed 38 trophies with United, as well as three Scottish league titles and four Scottish Cups with Aberdeen.
Sir Alex also managed St Mirren and Scotland, including at the 1986 World Cup, following a playing career as a forward which saw him finish top scorer in the Scottish Division One in the 1965-66 season while playing for Dunfermline.
In May 2018, he had emergency surgery for a brain haemorrhage after falling ill at home.
He recovered from the surgery and was given a standing ovation as he returned to Old Trafford in September that year.
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