The Rovers striker will have missed a week of his rehabilitation on his ankle when he makes his expected return to Cantley Park on Thursday.
Darren Ferguson admitted he hoped Williams would be ready to play in the rearranged trip to Stevenage, which has been pushed back to December 3.
And the Rovers boss says it remains to be seen as to whether Williams’ targeted return to action will be affected after his illness.
“We had pencilled in for Andy the 28th to start training again,” Ferguson told The Star. “He’s ill, he’s got food poisoning, which doesn’t help. It’s a nightmare.
Police incident Woodhouse Sheffield: Two men and a woman injured after large fight breaks out on Market Square
Sheffield fire: Crews tackle blaze in Wharncliffe Woods near Oughtibridge as heatwave continues
Sheffield fire: Video shows firefighters battling blaze at Wharncliffe Woods near Oughtibridge
Sheffield Crown Court: Here are the biggest cases from the last week including paedophile sting
Sheffield weather: Heavy rain set to lash city as Met Office extends thunderstorm warnings until Tuesday
“He won’t be back with us until Thursday and probably won’t start his rehab until Friday so he’s missed a week really.
“Whether that puts him back a week or not, I don’t know, but it certainly puts him back a bit.
“We were looking at getting a week’s training into him from the 28th, which would have got him ready for the Stevenage game.
“We’ve also got the Blackpool game in the Checkatrade Trophy between that and Plymouth.
“So we’ll wait and see on that.”
Ferguson admits it is touch-and-go whether Andy Butler will be fit to face Hartlepool United this weekend.
Butler was withdrawn at half time during Saturday’s win over Exeter City when his neck stiffened badly as a knock-on effect of the blow to his spine suffered the week before at Oldham Athletic.
“I don’t know if Butler will be fit for Saturday,” Ferguson said.
“He probably will be but he’s touch and go at the moment.
“We’re looking for him train on Thursday but he’s still a little bit stiff.
“I think he’ll be ok.
“It doesn’t help if someone plays and they keep having to come off.
“We need to be certain he’s going to be ok.
“He was a bit unfortunate that he got a knock early in the game in a similar area to the one he got at Oldham.
“It does take a lot for Butts to miss matches but he just couldn’t carry on.
“A bit of treatment and a bit of rest and you hope that he’ll be ok.”
Ferguson also confirmed Frazer Richardson will be out for the remainder of his short term deal with a knee ligament injury.