Celtic manager Martin O'Neill is recovering in hospital after undergoing a "small procedure", the Scottish champions said on Wednesday.
No details were given about O'Neill's operation, which came after the 74-year-old was in charge for Celtic's win against Dundee in their first game of the Scottish Premiership season on Monday.
Celtic expect the Northern Irishman to be released from hospital ahead of the club's trip to Kilmarnock on Sunday.
"In response to speculation, we can confirm that Martin O'Neill has undergone a small procedure in hospital," said a statement on the Celtic website.
"We would envisage Martin being released from hospital in the next day or two and on behalf of Martin, we would like to thank supporters for their kind wishes.
"We would ask that the privacy of Martin and his family is respected."
O'Neill signed a one-year contract in June to become Celtic's permanent boss for the second time after two interim spells last season.
He led Celtic to the Scottish Premiership title last term thanks to a dramatic final-day win against Hearts and also won the Scottish Cup.
Before the first of his interim stints with the Glasgow club, O'Neill had not managed since his spell with Nottingham Forest in 2019.
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