Jackson came off with a knock in Saturday’s 2-2 draw with Bolton Wanderers - replaced at half-time by Ethan Pinnock - and is facing a race to be fit for the trip to Elland Road to face former Reds manager Paul Heckingbottom.
Brad Potts is another doubt, although he should be fine to feature, according to Morais, who will definitely be without forward Mamadou Thiam.
“This is a game that everybody wants to play (in) and I think miracles are happening and everybody feels two days before the game that they are able to respond to the call of a manager,” said Morais.
“They want to be on the the field to play the game and I can feel the enthusiasm of the player and everyone else. They all want to be in the game and it is wonderful. Especially for someone like me who wants to make a decision about the best ones - the ones who can really give plusses before the game.”
Joe Williams is still at parent club Everton receiving treatment and it is unlikely he will return to the club before the end of the season.
Morais said: “I have not spoken with him since he went. I saw on Twitter or Instagram that he was saying thanks to the people that have helped him and he posted a picture of Heckingbottom and some team-mates.
“But I think that he has already said goodbye.”