Lee Johnson revealed that a sickness bug had swept through the Bristol City squad before their FA Cup victory over Premier League Huddersfield.
Josh Brownhill struck the 72nd-minute winner to settle a dour contest and send the Sky Bet Championship side into the fourth round.
"The team changed about 15 times in the hours before the game because we had a sickness bug in the camp," City manager Johnson said.
"We had at least four or five players in bed ill and some of the substitutes we had on the bench were never going to come on as they were ill too.
"There has been a horrible 24-hour bug going round and pretty much all the players have had it.
"Adam Webster has lost about half a stone but still played the full 90 minutes. It's been a tough week for him."
Brownhill was the Robins hero after Callum O'Dowda had headed against the crossbar in the first half.
The midfielder twisted and turned in a congested penalty area before rifling past Huddersfield goalkeeper Ben Hamer at his near post.
"Josh has felt like he has driven over a black cat this season, he's hit the crossbar and done everything but score," Johnson.
"I told him to hold in midfield and then he went and did that. I'll have to have words with him!
"I'd like another home draw next and if I'm being greedy I'd like a top six Premier League side.
"There were great events here last year when we played Manchester United and City in the Carabao Cup and we'd like that again in the FA Cup.
"If I had a choice I'd ask for Tottenham or Liverpool at home."
David Wagner owned up to Huddersfield's problems at both ends of the pitch after another dark day for the Terriers.
Substitutes Alex Pritchard and Steve Mounie both had second-half chances, but the Terriers lacked bite in front of goal before slack marking at the back was punished.
"We have another defeat and that's nine in a row now," said Wagner, whose side prop up the Premier League and are eight points from safety.
"We haven't had a clean sheet in that time and it hurts.
"It's not good enough. We have problems at both ends of the pitch.
"The performance was not at the level I think we are capable of.
"We were not good in ball possession and I was not happy with the way we defended.
"Bristol City got into our final third too easily, even if they did not create that many clear chances."