West Ham co-chairman David Gold is in hospital suffering from pneumonia, reports BBC Sport.
The 76-year-old, who spent several days in hospital in 2011 with septicaemia, is on strong antibiotics, said his daughter Jacqueline.
"I think he's learnt a very harsh lesson - not to go to football with bronchitis, he now has pneumonia. He is being assessed," she said on Twitter.
He attended West Ham's 2-2 home draw with Manchester United on Saturday but was taken to hospital on Tuesday night.