Sir Alex Ferguson was taken to hospital after falling unwell at Old Trafford shortly before Manchester United's Premier League match with Liverpool on Sunday.
Sources stressed it was a precautionary move for the 84-year-old former Manchester United manager, and not an emergency situation.
Ferguson, who managed United for 27 years during a glittering reign, watches the club's games from the directors' box.
No further update has been provided on his condition after his admission to hospital.
Ferguson had a brain haemorrhage in 2018 which left him seriously ill. Hespoke about his recovery in detail three years later.
He was pictured with guests at the stadium on Sunday a couple of hours before kick-off.
Ferguson was subsequently taken in an ambulance from Old Trafford to the hospital.
Club officials are optimistic Ferguson will soon be fit enough to return home.
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