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.
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