Midfield trio Cole Skuse, Teddy Bishop and Jay Tabb were all sent home from training and are set to miss the Portman Road showdown.
" There's a virus going around the place that is laying one or two of them low," said manager Mick McCarthy at his pre-match press conference
"I'm actually quite pleased because it knocked me low for about a week and I thought I was getting soft
It's made me realise that I'm not as soft as I thought I was when younger, fitter people have been affected.
"Of course, I'm not really that happy that they are laid up because they can't play
It's very unlikely that they'll be involved, but I think the other 14 are okay."
McCarthy will pick his side with one eye on the Sky Bet Championship promotion race - Town currently lie third, a point behind leaders Bournemouth.
"If you saw the team that we played at Southampton it will be similar to that," added McCarthy
"We made five or six changes and we competed very well.
"I am operating with probably 17 or 18 fit players
We've got Saturday, Wednesday, Saturday, we have some big games coming up, so it's probably right that I change my players around."
Bradford take on Millwall with the prospect of a trip to Chelsea awaiting the winners.
The Bantams are flying high in League One but saw a 10-match unbeaten run come to an end courtesy of a last-minute goal from Rochdale on Saturday.
Nevertheless, boss Phil Parkinson said: "We will take the positives and bring them into what is a massive game for us on Wednesday.
Ricardo Fuller could start for Championship strugglers Millwall despite reacting angrily to criticism from supporters during their weekend defeat at Blackpool
The Jamaican striker has apologised for his actions and manager Ian Holloway is ready to unleash him against the Bantams.
"I know how much he wants to help us win and that will be exactly the same on Wednesday," Holloway told the club website.
"The replay with Bradford is a huge game for the club and we need to stay true to our fantastic motto, 'stronger together'."
Source : PA