Geelong has been dealt a blow ahead of its top of the table clash with Port Adelaide with ruckman Dawson Simpson rolling his ankle at training.

Simpson injured the ankle at training on Friday and after a fitness test on Saturday morning was not given the go ahead to travel with the side.

Tall forward Josh Walker will be Simpson's replacement. Walker is currently leading the VFL's goalkicking after kicking two bags of four and one of three in the first three rounds of the VFL season.

Jesse Stringer has taken Walker's spot on the emergency list.