The former England international damaged his wrist in the home draw with Peterborough 10 days ago and is unlikely to figure for the rest of the season.
The 31-year-old has led the side to the verge of automatic promotion back to the Championship a year on from their relegation.
Lincoln are already confirmed as being promoted and Cardiff need four points from four games.
But they could grab the second automatic promotion spot if they can beat the Royals and fifth placed Stockport fail to win.
“Calum has had his damaged wrist assessed and there is no definite date on his return. I think he's going to be out for a while,” said Cardiff boss Brian Barry-Murphy.
“Dylan Lawlor is nursing a sore toe, but he should be alright, although Cian Ashford is out with a bad back. But we’ve got Isaak Davies is back in training, which is great.”
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It took a 95th minute goal from Yosef Salech, his first since returning from a neck injury, to clinch a 1-1 draw at Huddersfield in midweek.
That point has pushed the Bluebirds to the brink of promotion.
“We’re really aware of what we could achieve, but really clear that the only way we can achieve it is by winning on Saturday. It's pretty simple,” added Barry-Murphy.
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“When you've been in the game a long time you understand how difficult it is to be at the top of the table where we've been so often this season. It's a great experience for the team and the club really.
“I know the club hasn't been here for a long time and a lot of our players because they are so young are having to experience this type of situation for the first time.
"So, to go through it, feel what it's like, and to have to play the way we want to play is a great experience for us all.”
