Williamson damaged ligament during the 2-2 draw at Rochdale last weekend and the knee injury is likely to rule him out as Vale seek to clinch promotion for the second Saturday running.
Fellow striker Calvin Andrew and the versatile Rob Taylor will remain on the sidelines with knee and Achilles problems respectively.
However, winger Ashley Vincent, who has been sidelined for a month with an ankle injury, resumed training last week and could be in line for a return to the squad.
Vale will clinch promotion with victory. A draw will be good enough if Burton fail to win at Bradford.
"We all know the enormity of this game," Micky Adams told Press Association Sport. "We all know what's at stake. The players have seen the queues for tickets and they know what it means.
"We have a fantastic chance to create a bit of history, and I want to make sure we do. That is the motivation. Not that they should need any motivation, if they can't get up for this one then they never will.
"But at the same time there has to be discipline. We need to stick to the game plan. We have 90 minutes to win the game, we don't have to do it in the first 10 or 20.
"It's going to be a terrific atmosphere, everyone will be revved up. But we need to keep 11 players on the pitch. We don't need anyone doing something stupid."
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