The West Midlands outfit currently sit joint-bottom of the Premier League standings having accumulated just one point from their opening five matches.
As a result, O'Neil's position in the dugout is coming under scrutiny, particularly with Liverpool and Manchester City among their next three fixtures.
He was dealt a further blow last weekend when first-choice centre-back Yerson Mosquera suffered a serious knee injury that will keep him sidelined for the rest of the season.
Ahead of welcoming Arne Slot's Liverpool to Molineux on Saturday evening, O'Neil has revealed that more players are also in line to miss the game.
'Some will struggle for tomorrow'
Speaking at a press conference, O'Neil said that there was illness within the camp, making several players touch and go for the encounter with the Merseyside giants.
As quoted by Express & Star reporter Liam Keen on X, O'Neil said: "[Daniel] Bentley is fine now, but there's quite a bit of illness with players that will need a check. There's a virus going around and some players missed training today.
He added: "Some lads will struggle for tomorrow, but it's not definite. Bentley had his for a couple days before he felt better."
With Mosquera ruled out, Wolves are down to three experienced centre-backs, and O'Neil has admitted that he may have to risk the return of Toti Gomes from a thigh injury earlier than he would prefer.
O'Neil said: "We'll test him again in the morning. He's trained but he's not fully fit.
"He's getting closer. In an ideal world we'll probably leave him longer, but we'll see."
A back three or four?
As well as Toti, veteran Craig Dawson and Uruguay international Santiago Bueno are the other centre-backs in contention to start against Liverpool.
Alfie Pond, who struggled for starts on loan at Stockport County in League Two at this point last season, has also been promoted to the senior fold and started in the 3-2 defeat to Brighton & Hove Albion in the EFL Cup earlier this month.
O'Neill could also give consideration to switching to a back three, either using the aforementioned players or using of his midfielders in a deeper role.