Slaven Bilic spent two days in hospital this week with a severe bout of flu.
West Ham sources confirmed to Sportsmail that their manager checked himself into hospital on Sunday following Saturday’s 3-1 win at Middlesbrough.
He felt unwell before and during that match and went to hospital the next morning. He stayed in under observation until Tuesday and is now recovering at home.
The 48-year-old is not expected to return to the training ground before this weekend, with West Ham not in action again until Wednesday’s clash with Manchester City at the Olympic Stadium.