West Ham co-owner David Gold was in hospital being treated for cholangitis and septicaemia, the club have confirmed.
Gold, 74, was first taken ill on Wednesday evening and was unable to attend the Hammers' Barclays Premier League game against Liverpool.
His daughter, Jacqueline, said: "I saw my dad this morning (Sunday) and he is very poorly with cholangitis (inflammation of the bile duct) and septicaemia."
She added: "He is on powerful antibiotics and we hope to see an improvement in the next few days.
"He asked me to be at the Liverpool game today on his behalf and is absolutely devastated he could not be there himself."
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