Colchester United goalkeeper Ben Williams has revealed the extent of the illness which disrupted his pre-season.
The 29-year-old spent 10 days in hospital during July with a severe viral infection.
"If you have flu for a week you think 'a couple of days and I'll be fine'," he told BBC Essex.
"But I spent 10 days in hospital and when I came back even very light stuff like jogging made me very tired. That's not usually me."
He added: "Looking back I was out longer than I thought I would be."
The setback enabled Mark Cousins to establish himself between the posts for the U's, but after starting the first nine league games of the season, he suffered a shoulder injury, allowing Williams to return.
"My season starts now, it's a 35, 36-game season for me," said Williams, who has featured 89 times since joining from Carlisle in 2009.
"I'm hoping that after missing the first nine or 10 games I'll be in for the rest of the season."