Moore said attempts to treat the initial bite had not delivered the desired results, with Sheaf worsening the wound during a training ground tackle late in the week.
And the Arsenal loanee was then taken to hospital in order to fully remedy the problem and get him back ready and available for selection.
“Ben, we think, picked up an insect bite in the week,” Moore said.
“It was just around his hip and it got infected.
“We tried to treat it with some antibiotics but it just got worse.
“He went in for a slide tackle and took the skin off it. And it got infected further.
"We admitted him to hospital to get it cleaned out and administer some antibiotics. Hopefully that will clear it all up.
“It all happened on Friday so it ruled him out of the game.
“We hope to have Ben back in training in the early part of the week.”
Sheaf's replacement in the side, Madger Gomes, was withdrawn late in the game, apparently injured.
Moore said the midfielder had felt his muscles tighten and was brought off as a precautionary measure.