The loanee is suffering from a back issue and will be assessed ahead of the encounter with the in-form Lions.
The Portugeuse also revealled that Matt Mills is still sidelined with an ankle injury and is not sure when he will be back in the fray for selection again.
Morais said: “I am expecting to have some updated reports. What I know is that Williams has some pain in his back. But it is (getting) better and he rested all day yesterday (Wednesday).
“I don’t think that there are any other (fresh) injuries from what we have had in the past weeks and the other players are in condition to train.”
On the timescale regarding when Mills will be available for selection again, he added: “No, not yet.”
Barnsley are seeking their first win in 11 home games on Saturday when they tackle Millwall, with the Reds’ last Oakwell success coming way back on November 4.